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 MOFGA's 2010 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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Pest Report - June 8, 2010

Striped cucumber beetles are our most serious early-season pest in vine crops.
(Modified from article in Mass. Veg. Notes written by Ruth Hazzard & Andrew Cavanagh, University of Massachusetts, updated for 2010.) Striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris in field edges, and with the onset of warm days and emergence of cucurbit crops, move rapidly into the field. I am just receiving reports that the pest is appearing in south/central Maine. Densities often are very high, especially in non-rotated fields or close to last year’s cucurbit crops. Management cannot wait because adult beetle feeding on seedlings (cotyledons and young leaves) is the most serious, and can cause stand reduction and delayed plant growth. Also, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this may be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. By far, floating row covers offer the best results. You must get the row cover on at transplanting or seeding. Early management is important to avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.

Perimeter trap cropping gives excellent control with dramatic reduction in pesticide use (see following short article).

Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week for two weeks after crop emergence) and treat after beetles colonize the field. Early spot treatments of field edges can be helpful. The threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants. Less wilt-susceptible crops (butternut, most pumpkins) will tolerate 1 or two beetles per plant without yield losses. Spray within 24 hours after the threshold is reached. Proper timing is key.

OMRI-listed insecticides available for use in striped cucumber management include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). In 2009 spray trials comparing these three products at the UMass Research Farm, kaolin was the most effective in reducing beetle numbers and feeding damage. There was a trend toward Surround WP being more effective when Pyganic or Entrust was mixed with it, but never significantly better than Surround alone. Other studies have shown more efficacy from pyrethrin and spinosad. Remember, Surround should be applied before beetles arrive because it acts as a repellent and protectant -- beetles do not “recognize” the plant and so do not feed -- not a contact poison. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed before setting out in the field.

I just heard from a grower who tried out a vacuum yesterday and reported that it seemed to work well. He suggests using a vac with a low setting and/or a broad nozzle so that you don't damage plants. Also, do this earlier in the morning when they are sleepy and slow and be sure to look in their hiding places under the plants.

Over the past years, you have probably heard a lot from us about perimeter trap cropping to manage striped cucumber beetle in cucurbit crops. The system has proven itself as an effective, cost-saving method for managing this pest. Systemic or foliar insecticides in the trap crop border are effective in halting the beetles in the border and protecting the main crop. PTC systems can reduce insecticide use by over 90% if implemented correctly, but this is not the only benefit. By spraying only the border of your crop you’re leaving the main part of the field as a refuge for pollinators and natural enemies of insect pests. Leaving the main crop unsprayed may also help to delay the development of insecticide resistance in the striped cucumber beetles – a few beetles will always bypass the border, and thereby escape selection for resistance. The first trap crop that we looked at was Blue Hubbard, but many growers told us that Blue Hubbard is difficult to market and other border trap crops were needed. We evaluated buttercup and kabocha squash as alternative border crops, and they worked just as well as Blue Hubbard. Markets for these crops are strong. Any Cucurbita maxima variety is likely to be very attractive. This species includes many giant and specialty pumpkin varieties; the only one we do not recommend as a border crop is Turk’s Turban because unlike most C. maxima varieties it is highly susceptible to bacterial wilt which is vectored by the beetles. You can even plant a border of mixed C. maxima around your butternut squash, acorn squash, and other winter squashes that are C. pepo, or C. moschata types. This will provide you a wide variety of interesting squash to market. We’ve tested this system extensively and found that as long as the trap crop border is planted on good land and remains intact the system works remarkably well. In most cases, growers who use this system never need to apply insecticides to their main butternut crop at all. In Connecticut, they’ve found the system to work equally well with cucumbers and summer squash. Zucchini tends to be more attractive than summer squash, and some varieties such are so attractive that they could be used as a trap crop. We’ve also seen PTC work well in pumpkin crops, as long as the pumpkins in the main crop are C. pepo and not C. maxima. Remember, many giant and specialty pumpkins are actually C. maxima species, and would make good trap crops. On organic farms, growers often treat the main crop with kaolin clay (Surround WP) which serves as a repellent. For transplants, using this before planting is very efficient and lasts for a week or so if there are not heavy rains. Spinosad or pyrethrin could be used in the border. Every year we talk to more growers who adopt this system. The reduction in pesticide costs can be dramatic, and more than offset the small amount of time and care it takes to plant and treat a solid perimeter trap crop. If you would like to try this system and have any questions, or just want to find out more about how it works, please call Andy Cavanagh at 413-577-3976.

Mexican bean beetle larva (above) and adult (below).
(Reprinted from Mass. Veg. Notes, written by Ruth Hazzard). If Mexican bean beetles have historically been a problem on your farm, you will very likely see them again this year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report significant damage from these pests and have to take action to prevent crop loss. Using biological control can reduce the need for insecticides. Mexican bean beetle (MBB) adults are coppery brown with black spots. They look very much like large ladybeetles and in fact are closely related – but unlike lady beetles they feed on leaves, not other insects. Adults lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season, often with increasing populations in each generation. Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. This small (1-3 mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae. Planning 2-3 releases at 7-10 day intervals will help ensure good timing. and coverage on several plantings. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies. As with any biological control, make releases as soon as the pest is present – not after it has built up to damaging numbers. The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch. Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. If in doubt about the timing of the hatch, release as soon as you see the eggs – if you wait for the larvae you may be playing catch-up. The release rate should be at least 2000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more. The 2009 cost from NJDA is $40 plus shipping for 1000 adults, or $20 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge. Order adults if you already have MBB larvae in the field. Ship for overnight delivery. Instructions for handling and release will come with the wasps. Wasps reproduce in the field and will still be around when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost. Plan ahead by contacting a supplier to inform them of your expected release dates and acreage. Contact information for New Jersey source: Tom Dorsey, 609-530-4192; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628. http://nj.gov/agriculture/divisions/pi/prog/beneficialinsect.html. Pediobius is also available from the following suppliers: Green Spot Ltd., NH., www.greenmethods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-370-4301, http://www.biconet.com/. If you would like assistance in using these biocontrols in your bean crops please call the UMass Extension Vegetable Program at 413-577-3976 or 413-545-3696 or email at umassveg@umext.edu. --

No. Those are not cucumber beetles. Potatoes, tomatoes and sometimes eggplants are attacked by this pest that only superficially looks like a cucumber beetle. This is the Three-Lined Potato Beetle. The adult of this pest is about the same size as a cucumber beetle but has a reddish head and a thorax with two dark spots. The wing covers are dark yellow with three black stripes. Its favorite food in my experience is tomatillo.

The Three-Lined Potato Beetle overwinters as an adult and wakes early in the spring. They are there waiting for you to plant your solanaceous crops. The females soon begin laying eggs that hatch in about two weeks to larvae that look a bit like Colorado potato beetle larvae, except these critters have the endearing practice of carrying a small pile of their own excrement on their back. The larvae mature in about two weeks. There are probably two generations per year.

On most crops the level of the pest does not warrant control. If this pest has been a problem in the past, floating row covers will help you avoid the overwintering adults and that should get you by. Hand picking will work on small plantings. Pyganic and Entrust may offer some relief. Rotenone works well, BUT REMEMBER THAT THERE ARE NO ROTENONE FORMULATIONS THAT MEET ORGANIC STANDARDS.

Photo by Cheryl Smith, University of New Hampshire.
. At this time late blight is not reported in New England. There were reports in more southern locations, e.g., PA, but that seemed to be a localized event and not related to anything that is moving towards us. There have been no new reports recently. Of course, I will immediately get the word out when I hear about anything.

In the mean time, you should learn to recognize some other tomato problems. I have not heard about or seen these here yet either, but these are regular problems that will be here soon. Be ready and don't jump to the conclusion that you have late blight. Learn to recognize that too. If you are reading this as an email, you may want to go to the on-line version that has pictures. That is posted a few days later than the email goes out.

The three most common problems with tomatoes grown in the field in Maine are Early Blight, Bacterial (Spot and Speck) and Septoria Leaf Spot. It is early, but it is time to start looking if you want to get some control on them.

Early blight on tomato plant (above). Septoria leaf spot on tomato plants (below).
Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area effected. On the fruit black specks develop that rarely get larger than 1 mm . Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.

Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.

-Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.

Crop rotation is the first line of defense from these problems. Sanitation is important. Do not grow tomatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 12X dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops when they are wet. Scouting is going to be important this year. With wet weather, start early and if you decide to use a material, copper is probably the one most effective for us organic growers. If you decide to do it, start at the first sign of problems and you need to keep the new tissue covered. Still, because of problems with the way inert ingredients are regulated in the NOP Rule and the changes in the way EPA categorizes inert ingredients, Champ WG is one of the very few permitted formulations of copper for certified growers. Be sure to check with your certifier if using something other than that.

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