Eric Sideman's Pest Report
June 26th, 2000

I want to thank all the folks at UMO, U Mass and UVM who allow me to take items from their reports. And, I want more reports from our growers. Please take a moment to let me know of any critters or diseases you are seeing. Thanks to those of you who did send me info.

Crop Condition

Even though we have not had a significant rain in the state in more than two weeks much soil is still holding some water. But, if you are on high sandy ground you better check the irrigation equipment.

Pests

POTATOES

LATE BLIGHT ALERT! (adapted from Cornell Extension)

Special Note from Jim Dwyer:

Please dispose of all cull piles! Cull piles pose a significant threat to the entire Maine Potato Industry. Please recheck all buried cull piles for regrowth.

Late blight has been found in Albany County, NY on tomatoes (and on potatoes in Starksboro, VT). It is highly recommended for growers to have protective fungicides on their potatoes and tomatoes if the disease was prevalent on your farm or in your area last year. Long periods of high relative humidity and leaf wetness (from rainfall, dew, fog, or irrigation) are very favorable for late blight. The favorable temperature range is very wide, but the disease proceeds most quickly when average day and night temperatures are 59-80 degrees F. The higher the temperature, the more quickly disease progresses. The disease can knock down a field in 5 days if left alone. It is very important to scout your fields regularly, especially if the weather continues to be wet and particularly in poorly drained areas where high humidity hangs on. Late blight lesions are large, about the size of a half-dollar. In the morning, before the humidity drops, you will see a ring of white spores around the lesion which is dark gray to black. Sometimes, if protective fungicide sprays have been applied previously, you will not see the lesions on the leaf but late blight spores can germinate at the axle of the leaf to the stem, turning the stem black for an inch above and below the axle. If you see something that you think could be late blight, promptly send a sample to the Pest Management office, 491 College Ave, Orono, Maine).

Organic growers rely on crop rotation, but if you are in an area with lots of potential spores blowing around in the air, then several fixed copper fungicides are available (Basicop, Champ, Kocide, etc.) that provide control of late blight and early blight, IF used preventively. These and other copper products are registered for use on both potato and tomato.

Aphids From James Dwyer in the county;

Growers should be aware that winged green peach aphids have been found in our yellow pan water traps in Aroostook County. These are most likely the stem mothers that have hatched from overwintering eggs and are now moving to a summer host. However, we strongly encourage all growers to begin field scouting for aphids.

Colorado Potato Beetles: Colorado potato beetles have been emerging throughout our scouting range and are actively laying eggs. Watch these egg masses carefully. When about half of them have hatched it is time to spray one of the Bt products such as Novador or Colorado Potato Beetle Beater. Spray again in about 10 days. Then continue to scout the field for any new arrival of adults. Remember, the Bt does not effect the adults and works poorly on large larvae. It is important to keep on top of this pest and now is your best time.

POTATOES, BEANS, STRAWBERRIES

I have already seen adult leaf hoppers on beans in the Albion area. This is a very destructive pest that some years comes into the state in such numbers that some crops like beans and potatoes are totally destroyed. They do not overwinter in Maine but leap frog their way up from the gulf coast each summer, sometimes making it in big numbers and sometimes not. Be on the lookout and let me know if you see them in large numbers.

The potato leaf hopper is the most destructive on our crops. It favors alfalfa, beans, strawberries and potatoes. It is a bug that sucks the plant juices. The feeding causes curling, stunting and dwarfing accompanied by a yellowing, browning or blighting of the foliage know as hopperburn or tipburn because the damage is first seen at the leaf tips working inwards.

The leaf hopper is small (3mm), pale green and wedge shaped. They are very fast and often not seen by the grower until the damage is so great that the farmer finally looks carefully. It is too late then. Look now and continue looking on a regular basis. The best way to spot them is to run your hand over the top of the crop lightly brushing the leaves. If you have them you will see them hop quickly. If you have them bad you may see a cloud. Find one that lands and identify it. (Tarnished plant bugs also my flitter around, we will get to them next week or the week after. So far, they have not been bad this year). A better way to find the leaf hopper is with a sweep net if you have one. Later in the year you will see the nymphs, especially on the underside of leaves, that can run backwards and sideways. When you spray be sure to hit these too.

Crop rotation will not help control leaf hoppers. The only organic control that works for the leaf hopper is a concentrated pyrethrum spray such as Pyrenone or Pyronyl, which I know that Johnnys went out of there way to find. Only use these if you have a pest that needs it. These are broad spectrum, harsh pesticides that kill plenty of beneficial insects too.

CABBAGE FAMILY

(adapted from Ohio State Extension):

When scouting cabbage fields and closely examining leaves (including undersides) be on the lookout for larvae of cabbage worms. Diamondback moth larvae when fully grown are about 1/3 inch long, gray-green, relatively hairless, and wiggle when disturbed. Imported cabbage worm larvae grow up to one inch long, and have a faint yellow strip on their backside. Cabbage looper larvae grow up to an inch and a half long. They raise their body in a 'loop'. In the field, there can be extensive parasitism of these larvae and their cocoon-like pupae. Species of a tiny wasp called Cotesia can lay their eggs in these caterpillars, as well as in tomato hornworm. You may have seen the many small white silken cocoons of these wasps as they develop attached to a host caterpillar. If parasitized by the tiny wasp called Diadegma, the normally green diamondback moth larvae or their brown pupae are turned into a grayish white cocoon, sometimes with a distinctive white band. Several other species of parasitoid wasps attack caterpillar cabbage pests. Use of B.t. products (DiPel, Javelin, MVP, etc.) to keep pest populations in check is an excellent strategy for control at this time of year because it controls the caterpillars but does not harm the beneficial wasps that parasitize the caterpillars. Stay away from using botanical sprays such as rotenone or pyrethrum when you do not need them. To be most effective, B.t. should be applied when larvae are still small, with good coverage of all leaf surfaces (upper and lower). Use of a spreader-sticker is recommended with B.t. on crucifers.

CUCUMBER FAMILY

As soon as cucumber, squash, pumpkin and melons pushed through the ground these critters find them. I have heard that in some areas they have already caused extensive damage to seedlings. Crop rotation works fairly well, at least to delay the attack. They are pretty good fliers and usually will eventually find your cucurbits. Start looking for them now and keep it up at least until flowering.

Seedlings are particularly susceptible. As soon as they push through the soil the beetles attack them, eating off the stems and cotyledons. If the plants survive, later feeding on the leaves, vines, and fruits by adults and then larval mining of the roots. In addition, the beetles are vectors of the organisms that cause bacterial wilt, which can be more damaging then the insect.

The beetle is abut 6mm in length, yellowish green with 3 black longitudinal stripes. The adult passes the winter in shelter of plant debris. That is why rotation works. If you put your cucurbits back where they were last year the cucumber beetle is there to jump on them. Row covers work, especially to keep pests of the very susceptible seedlings. But, remember to lift the covers to weed and when flowering starts take the covers off for pollination. Covers of course will not work if you put the cucurbits right back in the same spot as last season.

When they find you you will have to turn to the big guns. Pyrenone or pyronyl are the two products that I know work best. Spray very early in the morning when the beetle is inactive in the cool air. When warm they will fly up and away as you walk down the row and return when you pass by. Pyrethrum, the active ingredient in the above formulations, is a contact insecticide. Be sure to spray the undersides of the leaves.

STRAWBERRIES

Black Vine Weevil Problems

Alan Eaton UNH Cooperative Extension

Many of you know that I have been evaluating strawberry fruit pest injury across the state for the last three years. Black vine weevil injury has been something we watched for while we visited the fields. The characteristic notching the beetles make at the edge of the leaves is easy to spot. We didn't make counts, but I noticed that the injury was easy to find in '97, compared to '98 and '99, when I found almost none.

Now it seems that I may have been lulled into a false sense of security by such early season checking. In the last 2 days, I have heard from 3 growers, all of whom I visited in my fruit evaluations. All have SERIOUS injury from root weevils. Another report came from southern Maine. What's going on?

There are several possible contributing factors, and I am going to speculate a bit on what they are. It will be a while before we can sort things out, but here's what I'm thinking. Possible contributing factors can be 1) warmer temperatures in fall (and winter?) 2) reduced effectiveness of our chemical option and 3) killing beneficial organisms that used to help. I'll fill in on a few details below.

Warmer Temperatures? Black vine weevil adults can survive our winters if they are mild, and there is a bit of protection. If temperatures in late summer and early fall are warmer than usual, then we would expect to see more adults surviving longer, laying more eggs, and laying them later in the year, compared to "normal" conditions. Normally the adults appear in July and start laying eggs in late July or August. Egg laying continues, following temperature patterns. Warmer temperatures mean faster development and more eggs laid.

Reduced Chemical Effectiveness? Two years ago conventional growers lost the registration of Furadan, but had another insecticide registered. The new material was Brigade, a pyrethroid. The new material was recommended to be used a bit earlier in the season, compared to Furadan. It also had the advantage that the pre-harvest interval was zero days. After talking with Dr. Rich Coles at the Connecticut Agr. Research Station, I learned that the adults can recover from the low labeled rate of Brigade --- they look like they die, but after a day or two, they walk off and return to laying eggs! He says you need the high rate. Also, I am concerned that we are seeing more problems with two spotted spider mites. Those are usually held in check by our native predator mites, which we know are nuked by pyrethroids. Killing Beneficials? Rich told me that his work with BVW in Connecticut suggests that ground beetles may be significant predators of black vine weevil (probably the larvae?). He also wonders if fumigation may kill many of the native insect-attacking nematodes in our soils.

Rich's work with nematodes suggests that they are a very effective option for BVW control in strawberries. If the correct species is applied, you may get substantial survival of the nematodes over the winter, continuing control next season. He recommends spring application (May), and Steinernema feltiae or Heterorhabditis bacteriophora as effective species that survive winter well. Missed the May application window? Application at the end of August may be effective. Of course, application of nematodes is affected by weather - you need to have moist soil conditions, or the tiny nematodes fry before they can penetrate down and be protected. Rich's message is: fear no weevil. This critter can be easily controlled with nematodes. Hopefully, we will see more on his results, and find out if they work as well here in NH, too.

Strawberry Root Worm: Strawberry root worm (Paria canella) is a pest that is becoming more common in New England. Infestations of this insect can contribute to stress induced decline or black root rot under certain conditions. Overwintered strawberry root worm beetles (the adult form of the insect) are found feeding on leaves at this time of year. They are small (1/8"), round, and copper colored with a dark pattern on their backs. They cause shot-holes in the leaves. The immature root-feeding grubs are also small (1/8"), creamy white in color with 3 pairs of legs, and are actively feeding on roots in the late spring to early summer. A lot of root damage can be done during that time. The new generation of adults appears after renovation (late July or early August). It is also possible that soil applications of parasitic nematodes mentioned above would be effective at controlling this serious pest.

Most organic growers use short rotations plowing under the field right after harvest and leaving fallow for a few weeks before cover cropping. This kills a lot of the root worm, clipper (the clipper was very bad earlier this year...it is the critter that clips off buds and leaves them hanging there dead with an egg in them) and other pests and exposes many to bird feeding.

(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.)