MOFGA Pest Report 2005
14 June

(View List Of All 2005 Pest Reports)

FLEA BEETLE

It is still wet in many locations, still too wet in some fields to have anything but the weeds out there. And where the plants are out and growing pests are beginning to come. One of these is flea beetles. Remember, there are different species of flea beetles so when planning rotations with crops or green manures keep this in mind. For example, the flea beetle that attacks the tomato family crops is a different species than the one that attacks brassicas.

In the autumn, adult flea beetles move into shrubby or wooded areas near fields where they have been feeding. Researchers at UMASS found the highest numbers in shrubby borders, somewhat fewer in the woods, and virtually none in more open grassy areas near the edge of the field.

Adults leave overwintering sites in April and early May, to feed, mate, and lay eggs. These adults are feeding right now. Newly sprouted potatoes and brassicas are getting hit hard. Row covers would have been a good idea, but if you did not cover it is too late now. Research has shown some efficacy from both Pyganic and Entrust. But, in most years, small plants out grow the damage done by the spring influx of overwintered flea beetles. That is most years, so you have to make the decision to treat or not.

Later in the season, eggs are laid in the soil near host plants, and larvae feed on root hairs and roots. After a pupal stage, new adults emerge from the soil. The rate of larval development is temperature-driven, so cooler soils will result in slower growth and delayed emergence of the summer adult generation. Depending on temperature, the new generation of adults will begin to emerge in mid to late July. Feeding during July may be quite heavy. There may be another generation, but more likely, these adults will head for overwintering sites in August and September.

THREE LINED POTATO BEETLE

The Three Lined Potato Beetle is also referred to as the Old Fashioned Potato beetle. I often get calls from people claiming that cucumber beetles are feeding on their potatoes. It only slightly looks like a cucumber beetle. Take a look at the following web sight for a picture:

This critter does much less damage to potatoes than the Colorado Potato Beetle. But it is hammering hard right now on tomatillo and other tomato family crops.

MANAGING COLORADO POTATO BEETLE

Colorado potato beetles (CPB) are moving into potato and eggplant crops, and will soon be laying eggs. Some adult beetles overwintered in the fields where the larvae completed development in the fall, but most spent the winter in the undisturbed habitats adjacent to these fields, where they burrowed into the soils below tree foliage up to a depth of 12 inches below the soil surface. In spring the beetles have to regrow their flight muscles before they are able to fly. At first they search for food plants by walking from the field edges where they overwintered. This is why field edges of non-rotated fields are attacked first. If beetles do not find host plants via walking they will engage in migratory flight, searching for host crops. Once host plants are found adult begin to feed and lay eggs. Some beetles mated the previous fall or late summer; hence they have no need to mate in the spring to produce viable eggs. They continue to mate in spring. The bright yellow eggs are laid in clumps that average 30-35 eggs, generally on the undersides of leaves.

Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from previous year's fields. Barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season. Also, the total population of adult beetles is lower, producing fewer larvae to control. The next (summer) generation beetles will emerge later, possibly after August 1st, in which case they won't produce a second crop of eggs.

Now is the time to scout for adults, eggs and egg hatch.

Walk your fields and look for CPB adults and eggs. Except for field edges in non-rotated fields, adult beetles do not usually cause enough direct damage to early potatoes to require control. The economic threshold for adult beetles in potato is 1 beetle per 2 plants (or per 2 stalks, in midseason). Damage to eggplant seedlings from adult feeding could be severe enough to warrant control of the adults even before eggs hatch, especially on field edges. Spot treatments may be warranted. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag the earliest egg masses you find with bright tape or flags, and then keep an eye on them until they hatch. Hatched larvae go through four stages before they become adults. In the first stage, the larvae are about the same size as the eggs and second stage, they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It's a good idea to prevent beetles from ever reaching the fourth instar! After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. About 10 - 14 days later the next generation of adults emerge.

Spray timing and thresholds and materials: If you are using Bt's (Novodor), you want to make the first application when 20-30% of the eggs have hatched, or when the oldest larvae reach the third instar. But NOTE: There are no Bt formulations for control of CPB that are permitted at this time on organic farms.

If you are using spinosad (Entrust, is the permitted organic formulation) or a broad-spectrum insecticide such as a pyrethrum such as Pyganic, you can wait till more larvae (grubs) are hatched.. Applications made with Entrust or Pyganic when the oldest larvae reach the beginning of the fourth stage (instar) (when they are about 1/3 inch long) will kill larvae that have hatched up to this point. I would only recommend a broad spectrum insecticide on an organic farm when there is a need to control another pest at the same time such as potato leafhopper. So, Entrust is the recommended material for CPB control on organic farms, when cultural controls fail.

The threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason), based on a count of 50 plants or stalks. Thresholds established in the Northeast for eggplants from seedling to fruiting stage include: 15 CPB per 10 plants (Rutgers) or 2 small/1 large larvae per plant (< 6 inches) or 4 small larvae /2 large per plant > 6 inches) (Cornell). In eggplant, in addition to defoliation, beetles sometimes clip the stems of flowers or flower buds. This directly reduces fruit formation and marketable yield. On the other hand, potatoes can tolerate 20% defoliation without reduction in yield (or even more, depending on time of the season and cultivar).

Control of the Colorado potato beetle with the fungus Beauveria bassiana (Mycotrol O (Emerald BioAgriculture) or Naturalis H&G (Troy BioSciences) has met with variable success, largely dependent on the population pressure and application methods. But many growers believe it does keep populations smaller over the years.

Pesticide Resistance: Colorado potato beetles have a phenomenal ability to develop resistance to insecticides. To a large extent, resistance develops on a field by field basis. That means that you have control over how resistant "your" beetles become to any given product. Management strategies for CPB should use crop rotation and alternate classes of insecticides in each generation of the beetle. To prevent resistance, it is recommended that farmers alternate among classes of insecticides in each generation, and throughout the season. For example, if you used spinosad, (Entrust), then it would be good to use Bacillus thuringiensis (Novodor) for the next spray. But, as we mentioned, Novador is not permitted on organic farms. So, the next best option is to spray Entrust as infrequently as you can. If you are spraying Pyganic for leafhopper, than do not spray Entrust since the Pyganic will give you good CPB control.

Since organic growers have very limited options for rotating pesticides with different modes of activity it is important to not try to kill every last beetle with Entrust. That would surely leave only resistant beetles to breed. This is especially true in the late summer. Remember that potatoes can tolerate more than 20% defoliation and so it highly recommended that growers leave lots of live beetles which will leave susceptible beetle genes in the population.

Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop of potatoes between overwintering sites and this year's crop and get it in earlier than the main crop; then control early-arriving beetles .

Natural enemies and cultural controls: Straw mulch placed around potato plants has been shown to reduce the number of beetles that colonize and feed in the crop, and reduces subsequent larval damage. Heavy mulches are more effective than a light mulch. There are numerous beneficial insects that have an impact on CPB, including larvae of the green lacewing, two-spotted stink bug and spined soldier bug, lady beetles especially the 12-spotted ladybeetle (slightly pink and elongated), and certain ground beetles especially Lebia grandis. The parastic tachinid fly, Myiopharus doyphorae, which lays its eggs in the larvae, also causes mortality. While these natural enemies are often not sufficient to keep CPB populations below damaging levels, their effects add up. Using insecticides that are less toxic to these natural enemies helps conserve this benefit that comes free of charge.

(Modified from an article in UMASS Vegetable Notes by- R Hazzard; also thanks to sources including: D Ferro, J. Mishanec, J Boucher UMASS Vegetable Notes, Ruth Hazzard, editor and Ben Hunsdorfer, Assistant Editor.)

CULTURAL AND ORGANIC METHODS FOR STRIPED CUCUMBER BEETLE CONTROL

(From UMASS Vegetable Notes)

Managing cucumber beetles is best accomplished by using a combination of cultural practices, with insecticides used in ways that minimize cost and environmental impact. Last week (Vegetable Notes, Vol 16:4, May 25, 2005), we wrote about managing striped cucumber beetle with conventional insecticides using foliar sprays or soil-applied systemics. This week we will discuss transplants, which are becoming more widely used by many growers, row covers, and information for organic growers on Perimeter Trap Cropping and on organic insecticides or deterrents.

Crop rotation: Because beetles spend the winter in field borders close to last year's crop, planting into the same field encourages rapid invasion by high numbers of beetles. Rotating to a field at a distance from last year's cucurbits reduces beetle numbers significantly. Of course, crop rotation has many other benefits as well - in vine crops, its critical for disease management. Any barriers between the fields - woods, buildings, fallow fields or other crops, roadways and waterways - help delay the arrival of beetles.

Using Transplants: Several studies in the Northeast have shown that three-week-old transplants, set out in the field at the same time as a direct-seeded crop, will produce not only earlier but higher yields. These studies were done with both summer and winter squashes. Transplants have multiple benefits. Germination of untreated seeds in cool soils can be spotty, while transplanting ensures a good stand. Transplants provide a jump on the weeds. Plants are bigger when cucumber beetles arrive so that they are less vulnerable to both feeding damage and to wilt. An insecticide or repellent can be applied to flats before plants are set out, making it less costly. Planting dates are more flexible - for some crops, it may be possible to delay planting until late June and avoid the worst of the beetles. Plants can be held inside to avoid late frost or wait until fields are dry (or wet) enough to plant. Of course, it is not advisable to hold transplants too long. If they are already flowering or have been stressed when they are set out, they tend to develop into small plants with early but small fruit. Standard seedling production methods work well for vine crops, but large cell sizes (72, 36 or 24) or peat pots are recommended as roots should not be disturbed when transplanting.

Row Covers
Floating or spun-bonded row covers are very effective barriers that keep beetles off the crop during the critical early growth stage. They have the added benefit of enhancing growth and reducing wind damage in the early season, for an earlier yield. Studies have also shown an increase in yield with row covers. Covers must be removed at flowering to allow for pollination. Wire hoops are very helpful, to prevent damage from abrasion; these are usually used on single rows, but can also be used under wide sheets of 15 or 25 or 50 feet. Black plastic adds to the warmth and helps to solve the problem of weed management under the covers.

Perimeter Trap Cropping (PTC)
A technique that is gaining popularity in the Northeast is planting trap crops around the border of the field. See April, 2005 issue for more details. Cucurbit crops that are being planted or transplanted in June (pumpkin, butternut, summer squash, cucumber) can benefit from using a perimeter trap crop, most likely Blue Hubbard Squash . The following suggestions for managing the border apply to organic and conventional growers, except that the choice of insecticides is much broader for conventional growers:

• Scout the trap crop at least twice weekly and spray the border with an insecticide (e.g., Pyganic) as soon as beetles are found. Don't wait for beetles to build up in the borders or chew them down. It is important to maintain healthy border plants. Scout again to determine if repeat sprays are needed in the border. 1 to 3 sprays may be needed as beetles continue to colonize.
• An alternative organic control, for those who don't want to use sprays, is suction. A reverse leaf blower can be used (at least twice weekly) to suction beetles off the border plants. One grower who tried this last year was pleased with the results and noted that the blower chopped up the beetles nicely and though it did some damage to the border plants it kept beetles out of the main crop.
• For diversified growers who don't have large acreage of any single cucurbit crop, it is possible to grow a mix of crops inside the border. However, watch out for relatively attractive crop that might need additional sprays. For example, zucchini is more attractive than summer squash and may need to be sprayed even if it is inside a blue hubbard perimeter.
• Where heavy infestations might be expected, such as borders along woods where beetles may have overwintered, use a wider perimeter of 2-3 rows.
• If you the amount of Blue hubbard needed for the border is far more than you need, consider using other C. maxima crops, such as buttercup, Red Kuri, Prizewinner, or Cinderella Pumpkin to create the perimeter border. A mixed border has worked well where growers have tried this approach.

Organic insecticides. Insecticides available for organic growers include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). Pyrethrin is primarily a contact toxin, while spinosad acts both as a contact and a stomach poison. None of these provides a highly effective 'knockdown" of beetle populations. No rotenone products are approved under the National Organic Program. Surround WP should be applied before beetles arrive because it acts as is a repellent and protectant -- beetles do not "recognize" the plant and so do not feed -- not a contact poison. It can be tricky to mix and use. One approach is to mix a slurry in a bucket and then add the slurry to the tank, as the dry powder can cake if added directly to the tank mix.

Another approach is to add the powder to water and allow it to settle slowly. Once the powder is fully wet, agitate gently. Regular agitation is needed during spraying. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active.

Transplants can be sprayed before setting out in the field. Surround can also be used on the main crop of a PTC system, creating a "push-pull" dynamic. Ensure good coverage of the foliage (it will look like it was sprayed with white latex paint), including, if possible, the undersides of leaves (not easy when cotyledons are close to the ground). Reapply after a heavy rain and on new growth. And, wear a respirator or mask when mixing and spraying. Although kaolin is very safe in terms of skin exposure or ingestion, handlers should take precautions to avoid breathing the powder.

--Ruth Hazzard

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)