What to watch for: caterpillars everywhere!

Caterpillar feeding on developing blueberry buds. Photo: Bill Cline

Worms or caterpillars, whatever you prefer to call them, there is an bumper crop of larvae in North Carolina this spring.  My colleague, Steve Frank, ornamental and urban horticulture entomologist, spoke to the Raleigh News & Observer this week about about the large number of cankerworms present in state, and this afternoon, I received calls about caterpillar damage in two crops, blueberries and strawberries.  The abundant caterpillar populations are likely due to warm spring weather; many insects have been able to begin an early generation. In blueberries, this has resulted in isolated pockets of large numbers of what appear to mixed populations of spanworms, cankerworms, and other generalist caterpillars.

A diverse assortment of caterpillars from southeastern North Carolina blueberries. Photo: Bill Cline.

 One grower who has noticed large caterpillar populations in Reveille, a later flowering variety, and asked plant pathologist Bill Cline what the potential management options might be.  In the past, blueberries grower may have used malathion, a broad spectrum insecticide, applied in the late evening to control caterpillar populations.  I instead suggest that the grower use a narrow spectrum material that is safer to bees, as the plants to be treated were close to bloom.  Regardless of how safe a pesticide may be for bees, if plants are to be treated during bloom, any material should be applied in the evening minimize exposure to bees and allow for maximum dry time before they begin foraging.

The second question was from a research station in Virginia, where they had noticed green caterpillars present in their ripening strawberries.  My suggestion for strawberries would be the same--select a narrow spectrum, bee safe material.  These would include microbial (such as Bt) or insect growth regulators (such as Intrepid). See a note on pesticide recommendations.  Following any treatment, plants should be carefully scouted for re infestation, since high insect pressure situations may result in more movement into crops.  Just because caterpillars are present in a crop again following treatment does not necessarily mean that the treatment did not work.  Insects can also move back into plantings following a treatment.

Tolerance to organic controls observed in California SWD population

Mark Bolda, Santa Cruz, Monterey & San Benito UC County Farm Adviser, has reported on recent laboratory assays conducted in California demonstrating tolerance to Pyganic (pyrethrins), an organic insecticide used against spotted wing drosophila (SWD). The assays were conducted on a population that had been treated in the field with Pyganic many times.

Organic management tools for SWD are very limited. Entrust (spinosad) and Pyganic (pyrethrins) are the two most effective organic control methods, but both have short residual control times and must be applied frequently. This means that SWD are exposed to pesticides over multiple generations, which is a recipe for resistance development. The same situation exists with conventional insecticides, but there are more modes of action available to rotate, which lessens the likelihood of short term resistance development.

The two-year period from SWD detection to potential pesticide tolerance development is definitely short term and only highlights the fact that we need to manage SWD on a system-wide scale: optimizing non chemical/cultural management to reduce populations, wisely selecting pesticides, and rotating modes of action.

More information
Suspected Tolerance to Pyganic (pyrethrin) Found in Spotted Wing Drosophila - Strawberries and Caneberries Blog

Mid season tobacco pests & the burning question of tank mixes

Tobacco budworm moth.  Moths lay their eggs in or near tobacco buds and flowers and are more attracted to flowers. Photo: HJB

Tobacco budworm populations have been booming in our research plots this summer, and as they often are, tobacco budworm larvae are present in fields at or near topping.  The logical questions that follow these tobacco budworm populations is whether or not they need to be managed.  In general, if plants are within 2 weeks of toppping or large enough that contact sucker controls are being applied, tobacco budworm treatments are unnecessary.  This is because budworm larvae prefer to feed on flowers and seed capsules when given a choice between these and leaves.  These are the same plant parts (along with the youngest, smallest leaves) that are removed during topping. Tobacco budworm feeding during the interval between buttoning (when the unopened flowers are visible outside of the bud) and flower does not damage plant tissue that will be harvested and has no economic impact.  Therefore, any insecticide applied at this stage for tobacco budworm is a waste.  Tobacco budworm will not reinfest tobacco after topping because the attractive buds and flowers are no longer there.

Tank mixing insecticides and sucker controls
Among some North Carolina tobacco growers, it has been standard practice to include an insecticide (most commonly acephate) in the first few applications contact sucker control.  Contact sucker control materials are pesticides that, as their name implies, need to come into contact with a leaf axil in order to inhibit growth.  Contacts are typically fatty alcohols, or soaps, which are commonly made from petroleum or, in the case of organic contacts, palm oil.  Fatty alcohols are also used in a number of industrial and cosmetic applications.

Foliar (sprayed on) insecticides in tobacco should only be used when insects are present at damaging levels (the economic threshold).  Acephate is a broad spectrum insecticide, so it could potentially be used against a wide range of insect pests.  The insect pests most commonly present at or near topping are tobacco budworm, the "tobacco form" of the green peach aphid, and, less commonly, tobacco & tomato hornworms.  We already know that pretopping treatments for tobacco budworms are not needed, but what about aphids and hornworms?

Aphids
Aphid management in tobacco has shifted dramatically in the last 15 years.  Aphids used to be frequent pests which often reached treatment threshold (10% or more of plants with 50 or more aphids in the upper third) several times in a season.  The widespread (over 90%) use of systemic neonicotinoid insecticides (imidacloprid & thiamethoxam) has rendered aphids infrequent early season pests who typically only appear near topping.  If aphids are present in a field when contacts are being applied, it may be tempting to include an insecticide in with these materials, but this is totally unnecessary.  Contacts (soaps) can be excellent aphid control materials, because they dry out their soft bodies, and the application method for contacts actually results in decent coverage for aphid control.  In addition, aphids are less attracted to tobacco leaves as they "harden off" following topping and will rarely reinfest.  In an organic aphid management trial we conducted in 2009, none of the organic insecticides were effective against the large aphid populations present, but as soon as the grower started spraying organic contact and topping, the aphids disappeared.  Timely topping and good sucker management can eliminate an aphid problem, so insecticides in the contact do not provide any additional benefit.

Tobacco & tomato hornworms

Tobacco or tomato hornworm eggs.  Hornworm eggs are laid on the upper surface of tobacco leaves. Photo: HJB

Tobacco hornworm (Manduca sexta) larva, note the red posterior "horn".  Tomato hornworm larvae will have a dark blue horn. Photo: HJB

Tobacco and tomato hornworms typically occur in their highest numbers just after topping and, from a timing stand point, are perhaps the most logical insects to be targeted by an insecticide tank mixed with contacts. However, I do not recommend tank mixing insecticides with sucker control materials even for hormworms for two important reasons:

1. Phytotoxicity may occur when insecticides are tank mixed with oils and soaps, and more importantly, 

2. Contact sucker controls and insecticides should be applied to different parts of the plant and will be less effective with different coverage patterns.

The only time I have seen phytotoxicity associated with some of our newer, caterpillar active insecticides in tobacco is when they have been used in combination with contacts.  Although I have never seen truly damaging phytotoxicity associated with either Belt or Coragen, it doesn't make sense to combine these with sucker controls.

Because contacts need to coat leaf axils to be effective, they are applied in a coarse spray, run down spray, sometimes using modified hoods, as described in the 17 June issue of the Tobacco Connection Newsletter.  This application method drives contacts down the stalk, but hormworms are leaf feeding insects and could be missed with a stalk spray or hood application.  If an tank mixed insecticide application fails, it means yet another treatment across the field.  I would rather see one insecticide trip made, done correctly.

Stink bugs

A midseason tobacco ecosystem, tobacco budworm larva and adult brown stink bug.  Hoke County, NC. Photo: HJB

The last tobacco insects that may pop up in the mid season are stink bugs, both brown and green.  Stink bugs feed on the stalk and mid veins of tobacco leaves, which can cause them to wilt.  This damage is rarely, if ever, economically significant, and insecticide treatments for stink bugs are not recommended. In fact, so few insecticides are effective for stink bugs, that is unlikely that any of the materials with workable preharvest intervals would provide control regardless of whether treatment was needed.

Tobacco plant with leaf injured by stink bug feeding, Raeford, NC. Photo: HJB

More information
Tobacco Connection Newsletter, 2(6). 17 June 2011.

What does the "Dirty Dozen" mean for IPM?

The Environmental Working Group's (EWG) annual "Dirty Dozen" list of the produce most likely to contain pesticide residues has been released.  As it has in past years, the list contains several fruits, including apples (1), strawberries (3), peaches (4), imported nectarines (6), imported grapes (7), and blueberries (10).

The Dirty Dozen list often receives significant media attention, and most balanced articles typically point out that pesticide residues measured and regulated by the Environmental Protection Agency and that fruits and vegetables are important part of our diet which should not be eliminated or reduced because of pesticide concerns.

Pesticides, as their name makes clear, are used to manage (kill) crop pests, but the meaning of lists like the Dirty Dozen in the context of pest management is rarely, if ever, discussed.  To understand what the Dirty Dozen might mean for integrated pest management (IPM), it's important to understand what is meant by the pesticide use and pesticide residues.

Methods for measuring pesticides
The EWG used several factors when considering pesticide usage on crops.  These included the percentage of samples testing positive for any pesticide residue, the percentage of samples with more than one pesticide residue, the average number & quantity (ppm) of pesticide residues, and the maximum & total number of pesticides found in samples.   Data compared were from routine United States Department of Agriculture (USDA) testing.  Residues measured are of materials registered for use on the crops, and residues of registered materials are regulated by EPA.  In other words, legally allowable residues of pesticides registered and legally used on crops were measured, and these legally allowable residues have been determined by EPA to be safe.


The Dirty Dozen & IPM
While the number of pesticide residues present can certainly be an indication of heavy pesticide usage, it may also be related to a sound pesticide rotation as part of a resistance management program. It is actually worse for the environment and the farmer to use a single pesticide against all pests for two reasons:
1. Pesticides that are effective against many pests are called "broad spectrum" and are also often toxic to non target and beneficial organisms. In other words, broad spectrum materials can kill things we don't want to kill. When narrower spectrum or species specific pesticides are available, these are a better choice.
2. A single pesticide used against a species that has more than one generations per growing season (like SWD)

For these reasons, samples with more than one pesticide residue or relatively large numbers of different pesticides present are not necessarily troubling in the context of IPM.

Where I think IPM practitioners can learn from lists like the Dirty Dozen, however, is with respect to residue quantity and maximum residue levels.  It is important to stress, again, that the materials detected are legally registered and used on fruits and vegetables.  Produce with detectable levels of unregistered pesticides would not be allowed to be sold.

However, my goal as an applied entomologist is to develop integrated insect management strategies, of which pesticides may one, but not the only, tool.   Fruit crops where relatively high levels of pesticides are detected suggest that few non pesticide options exist.  This is a challenge and an opportunity for applied research.  This is a call to arms to develop management tools which reduce our reliance on pesticides in strawberries, blueberries, and the rest of the Dirty Dozen.  Just as consumers should not be afraid to eat the produce on this list, growers and scientists should not be afraid of the information it contains and should take this as an opportunity to improve our production systems.

Sound applied research takes time, but one project already underway was highlighted in South Carolina at an agent-training tour I participated in.  Spearheaded by Dr. Natalia Peres, University of Florida, with cooperators in the Carolinas, this project uses weather data to predict when strawberry fungal disease can infect fruit and only recommends pesticide applications if conditions are right for infection.  In test locations, this has resulted in a significant reduction in pesticide usage when compared to a standard, weekly spray schedule.  This type of pesticide reduction is exciting but is the result of years of previous research.  It is important that the need for meaningful, applied research is not lost in discussions of food choice and food security.

It is important to be conscious in our food choices, but it is just as important to be conscious of the infrastructure needed to support the ability to choose.  The importance of applied agricultural research has not diminished in the current era of budget tightening, but it is being pushed to the edge of priorities. This decreased support directly limits our ability to respond to public concerns like the Dirty Dozen and its list cousins.

What to watch for: When treating for SWD

Female SWD on raspberry at the Upper Mountain Research Station, Summer 2010. Photo: HJB

As spotted wing drosophila (SWD) is detected in more and more locations throughout the southeast (Georgia, Florida, 4 locations in South Carolina, 13 locations in NC), many small fruit growers are treating their crops. See here for lists of registered pesticides in blueberries, grapes, strawberries, and caneberries. For several reasons (efficacy, cost, and preharvest interval), organophosphate and pyrtheroid insecticides are among the most commonly used materials against SWD. The current management recommendations for SWD are weekly pesticide applications, rotating modes of action, beginning when fruit are ripening and stopping at the end of harvest and increased sanitation (frequent & thorough harvest, cull removal & destruction). These management recommendations represents a potentially large increase in pesticide use, at least in the short term, in these small fruit crops.

While these classes of insecticides are effective against SWD, they come with risks as well. The key risk, from a pest management stand point, is non target impacts on other pests and beneficial insects. While we we cannot anticipate all of the non target impacts, some are clearly likely.

The most likely non target effect of SWD treatments is the possibility to flare spider mites.

Twospotted spider mite female and eggs. Photo: HJB

Spider mites are economically significant pests of strawberries, grapes, and caneberries (raspberries moreso than blackberries). Both organophosphate and pyrethroid insecticides have been documented as flaring spider mites.

Strawberry, grape, and caneberry growers should scout their plantings for spider mites prior to beginning SWD treatments. A good rule of thumb is to observe at least 10 leaves or leaflets per acre or per variety block, if they are smaller than an acre. Spider mites can be observed and counted with a 10x hand lens. If spider mites are present, planting should be treated with a miticide before beginning organophosphate or pyrethroid treatments. North Carolina blueberry growers more commonly use these insecticides are rarely, if ever, have issues with spider mites, and I do not anticipate a need to manage mites in blueberries.

Spider mites may not be the only non target (unintentional) pest made worse by SWD treatments. Organophosphates and pyrethroids are broad spectrum materials, meaning they kill many different types of insects, including beneficial predators. The insects these predators may control could increase in their absence, but we cannot necessarily predict which insects these may be. Growers treating for SWD should be vigilant and scout their fields at least weekly to assess whether any new or unexpected insect or damage is present.

Tobacco budworm update

Calls about tobacco budworm have begun in earnest this week, and the main questions I am hearing are "What is the difference between Belt^TM(Bayer CropScience) and Coragen® (DuPont)?" and "I used Belt^TM/Coragen®, how long should I wait before I decide if I need to treat again?"

First instar tobacco budworm larva in eastern North Carolina tobacco. Photo via Loren Fisher.

What is the difference between Belt^TM and Coragen®?

Belt^TM and Coragen® are two recently registered insecticides for use in tobacco against Lepidopteran (caterpillar) pests. Both these insecticides share a common, and novel, mode of action. They act on ryanodine receptors, which form calcium channels in muscle cells, and inhibit muscle contraction. The Insecticide Resistance Action Committee (IRAC) places both of these materials in Group 28 (ryanodine receptor modulators). In other words, Belt^TM and Coragen® kill insects in the same way and using one following the other does not represent a rotation.

In our research trials over the last 3 years, Belt^TM and Coragen® perform similarly to one another when applied as foliar treatments. They also perform similarly to the standard insecticide used for tobacco budworm control, Tracer (spinosad, Dow AgroSciences). The key difference between Belt^TM and Coragen® is the potential in-plant movement of the latter. Coragen® is xylem mobile, which means that it moves in the plants water channels when applied to the soil. Coragen® has a transplant water label in tobacco, but our data on the efficacy of this application method is limited.

I used Belt^TM/Coragen®, how long should I wait before I decide if I need to treat again?

Both Belt^TM and Coragen® slow or stop feeding quickly. However, larvae may appear alive, but sickly (or moribund) for up to 4 days after treatment. Another insecticide application should not be made until sufficient time has passed to allow for the insecticide to work. If another treatment is considered necessary, growers should be sure to rotate to another mode of action.

As always, when I discuss treatment thresholds (10% infestation) for tobacco budworm, it is important to understand that these thresholds are very conservative, meaning that yield loss has rarely been documented due to budworm feeding, even at much higher infestation rates than 10%.

More information

A note about pesticide recommendations

What to watch for: Tobacco budworm

First instar tobacco budworm larva in eastern North Carolina tobacco. Photo via Loren Fisher.

Tobacco budworm populations developing
Tobacco budworm (Heliothis virescens) larvae are beginning to show up in North Carolina tobacco fields. At our research plots at the Upper Coastal Plain Research Station, Rocky Mount last week, we found several infested plants, and yesterday at the Lower Coastal Plain Research Station, Kinston, plots were between 0-10% infestation in most of our trials. The vast majority of the larvae present were recently hatched 1st instars, although a few 2nd instars were also present. This means that egg laying occurred fairly recently and that growers will likely begin to see tobacco budworm larvae in their fields soon. In fact, a consultant called Loren Fisher and I last week to report that he and his staff were seeing budworm larvae in fields in eastern NC. Populations in these fields were near treatment thresholds (10%). As always when I discuss treatment thresholds for tobacco budworm, it is important to understand that these thresholds are very conservative, meaning that yield loss has rarely been documented due to budworm feeding, even at much higher infestation rates than 10%.

Campoletis sonorensis wasp searching for young tobacco budworm larvae, Kinston, NC. Photo: HJB

Natural enemies present

Also present in large numbers at the Lower Coastal Plain Research Station yesterday were large number of red-tailed wasps (Campoletis sonorensis) in search of young tobacco budworm larvae to parasitize. The wasps were so common that it was almost easier to follow them from plant to plant than to search for the newly hatched larvae in buds. The large numbers of parasitic wasps also suggests that many of the larvae we saw this week may not make it to adulthood.

Management

For those growers whose fields have tobacco budworm populations at greater than 10% infestation in small plants, have not observed parasitic wasps, and plan to treat, there are several insecticides available (see the NC Agricultural Chemicals Manual for specific recommendations). Some NC growers have used Coragen (a newer insecticide from DuPont) as a transplant water treatment for preventative control of tobacco budworm. Because there is relatively limited data against tobacco budworm using this application method of Coragen, I cannot say how effective or long lasting its activity may be. It also important to note the size of tobacco budworm larvae feeding on transplant water Coragen treatments. First instar larvae may not have fed on enough tissue to kill them, so growers should hold off on making foliar treatments until 2nd instar larvae are present. Caterpillars eat the vast majority of the leaf tissue they will consume as large larvae, so the injury caused by a 1st instar as it develops to a 2nd will not be significant. However, if growers who used Coragen in the transplant water for tobacco budworm control have 2nd instar larval populations above a 10% infestation level and need to apply a foliar, rescue treatment, they should select a different mode of action material, such as Tracer/Blackhawk (spinosad), Denim (emamectin benzoate), Orthene (acephate), or methomyl (Lannate). Growers who have used Coragen in the transplant water should not apply Belt or Coragen as their first foliar treatment following transplant.

The future of endosulfan in small fruits and tobacco

In June, the EPA moved to terminate the use of endosulfan (an organochlorine insecticide). Among the crops I work on strawberries, blueberries, and tobacco will be potentially impacted by this termination. Endosulfan (trade names include Thiodan, Thionex, and many others) is registered for use against cyclamen mites, aphids, lygus bugs (strawberries); blueberry bud mites (blueberry); aphids, green June bugs, and stink bugs (tobacco).

This termination will mean different things for these different crops.

For tobacco, little will change. We have not recommended the use of endosulfan in tobacco for the last 4 years, because of pesticide residue concerns among buyers and because good, effective alternatives exist for the target pests. If the current agreement holds, no endosulfan can be used on tobacco after July 31, 2012, with sales restrictions taking effect sooner.

In strawberry, the same timeline also applies. No endosulfan can be used after July 31, 2012. We have removed endosulfan from the 2011 Southern Region Small Fruit Consortium Strawberry IPM Guide (update to be published this winter). Endosulfan is registered for cyclamen mites, aphids, and lygus bugs in strawberry. The UC IPM guide for strawberries recommends Kanemite and Agri-mek for cyclamen mites, both of which are also registered in NC strawberries (a note about pesticide use), and we have several tools for use against aphids. Lygus bugs are a trickier proposition. Pyrethriods are effective, but may have undesirable non target effects on mites (they may flare them). However, our spring strawberry season is typically complete before large lygus populations appear. Lygus, or tarnished plant bugs, have greater pest potential in day neutral, ever bearing, or perennial strawberry production.

Finally, of the crops I work on blueberries face the greatest challenge with the removal of endosulfan. Blueberry bud mite, BBM, (Acalitus vaccinii) is difficult to control in some varieties, and endosulfan is the only conventional material available. The pest severity of BBM varies by variety, and can be mitigated in the southeast with post harvest pruning. This is not an option in areas with shorter growing seasons. In recognition of the greater difficulty imposed by the loss of endosulfan on blueberries, there will be a longer phase out. Again assuming the current agreement holds, blueberry growers will be able use endosulfan until July 2015. This will give researchers and regulators time to develop and/or register alternatives to endosulfan for blueberry bud mite.


More information
EPA action to terminate endosulfan

Coragen now labeled for use in NC tobacco

The newest edition of the NC State Tobacco Connection Newsletter is now available. In this issue, I have 2 articles. The first discusses preplant insecticide uses and the second details the use a newly registered pesticide on tobacco, Coragen (DuPont).

Tobacco budworm (Heliothis virescens) is one of pests of tobacco for which Coragen is labeled. Photo: C.E. Sorenson.

Adapted from NC Tobacco Connection. 1(2): 9 April 2010
Coragen® labeled for use on NC tobacco
Coragen® insecticide (Rynaxypyr® or chlorantraniliprole), from DuPont, has recently been registered for use in tobacco in North Carolina. Coragen is the second Group 28 (ryanodine receptor inhibitor) insecticide to be registered for use in tobacco, with BeltTM (fluebendiamide, Bayer CropScience) being the first registered in the group. Both Coragen® and BeltTM act on insect muscles, resulting in feeding cessation and death.

Because Coragen®’s registration timing was unsure when the 2010 Flue Cured Tobacco Guide was produced, this article provides information on this new insecticide in comparison to our standards. You can find the supplemental label for Coragen® on tobacco: http://www2.dupont.com/Production_Agriculture/en_US/label_msds_info/labels/R1090.pdf. Two application methods are labeled, foliar and transplant water applications, and the rate range is 3.5 to 7.5 fl oz/acre. We have compared a range of foliar application rates of Coragen® to Tracer (spinosad, Dow AgroSciences) and BeltTM, and found them to be as effective to these materials. DuPont is recommending a rate of 5 fl oz/acre for foliar applications of Coragen®, and at this rate, this product should be at least as effective as Tracer or BeltTM¬ . We anticipate a greater degree of residual control with both BeltTM and Coragen® than we currently see with Tracer or Orthene (acephate), two of our standard foliar insecticides. We conducted longevity trials on these products in 2009, but we need at least one more year of data before we can draw conclusions. For the time being, I recommend good post treatment scouting with the anticipation that additional treatments may not be required. Good scouting is always of benefit, because in some years, no budworm treatments may be needed, and in 2009, several locations did not need to treat for hormworms because populations were late and smaller than normal. Scouting will also allow to maximize the potential savings of these products by reducing the total number of treatments if continued suppression is observed.

For growers interested in transplant water applications, DuPont is recommending 7 fl oz/acre in a minimum of 100 gallons per acre, or 2 fl oz/plant. Water volume is important, and I would not recommend using any less than 100 gal/acre for a transplant water application of this or other insecticides. Not only are smaller volumes much more difficult to calibrate, they may not adequately wet the root zone. We have included transplant water treatments of the active ingredient in Coragen® in research trials, but at a lower rate than 7 fl oz/acre. In these trials, we saw very good control with transplant applications, but again, the data are limited.

I have gotten several questions from agents and growers about transplant water tank mixes with fertilizer and other insecticides (such as Admire Pro or Platinum). I do not anticipate issues with combining Coragen® and Admire Pro or Platinum. We have combined these materials in research trials and have observed no adverse plant effects. We have not, however, combined Coragen® with a fertilizer tank mix, so although I also do not anticipate an issue with this application method, I cannot speak from firsthand experience. No matter how many research methods we come up with, growers always devise new ways to use a material, so we will be exploring some of these questions in 2010 at both grower and research station locations.


You can read the entire newsletter here: NC State Tobacco Connection Newsletter

A note on pesticide recommendations

Hands down, the most common question I am asked as an extension specialist is "what do I spray to control X?" I knew this would be the case from the get-go, and I enjoy helping growers and the public make good decisions about what, when, and how to use pesticides on their crops. That said, this blog will not be a forum for making those recommendations. Pesticide labels change frequently and vary by state. Because I don't know where you (hopefully there's a you) are from, what's available in NC may not be available or legal for your use. NC residents can refer to the NC Ag Chem Manual for recommendations for specific crops or can contact me directly for more detailed information. Interested parties outside NC are welcome to also contact me, and I will do my best to put you in contact with the right folks for recommendations in your state.