Eric Sideman's Pest Report
August 21, 2000

Pest Report for August 21, 2000

Crop Conditions

Late summer crops are coming in, though later than normal . Unseasonably cool temperatures returned last week...night temperatures in the 40s. Market demand outstrips supply in many farmstands and other outlets. Growers report running out of sweet corn and tomatoes on many days- unheard of for mid August! Rainfall was above normal again and some fields are soaked. Most farmers I have talked to have run irrigation very little this year. Last week brought more long periods with continuous leaf wetness. As a result, foliar and fruit diseases are blossoming. Some reports of whole fields going down to disease are coming in. Rotated fields and lighter soils are showing a significant benefit. Some growers are faced with deciding whether, or when, to cut their losses and disk under crops that are too heavily infected to be likely to produce marketable crops. Getting infected crops underground can speed decomposition and reduce aerial movement of spores to surrounding areas. Looking hard for some good news! Everyone is hoping for a turnaround to warmer, drier weather, but it is getting late to salvage the season for some growers. Others are doing quite well with long and great harvests of cool weather crops.

JAPANESE BEETLES

Japanese beetle adults are about half an inch long, with a metallic green head. The wings are shiny copper or bronze color, and there are a few tufts of white "fur" along the side of each wing when it is folded back over the body. They are commonly seen feeding during the day on many different crops. Their favorites are roses, raspberries and soybeans Life cycle. The life cycle of the Japanese beetle fits most of the species of grubs we encounter in New England, with minor variations depending on the species and the location. They have a one year life cycle, with adults emerging in mid July in most of Maine (slightly earlier further south and slightly later further north). The adults of Japanese beetle are active in daylight and begin feeding on many different kinds of plants, including in addition to their favorites mentioned above, asparagus, grapes, lindens, purple-leafed plums, and crabapples and vegetables such as corn (on silk perhaps causing poor pollination), peppers, green beans, collards, basil, and other herbs and greens.

The females return to the soil (often in or near wide expanses of turfgrass) and lay eggs, usually beginning in late July. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads about half the size of a June beetle grub when full grown). The first grubs usually appear around late July or early August and begin feeding on roots of grasses and other plants (especially corn). After about two weeks of feeding, the grubs molt to a second "instar", and feed for another three weeks. The grubs molt once more, to the "third instar" (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs begin to migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks. By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.

Japanese beetles are the most common and widely distributed scarab species in New England. They are slowly moving north through Maine. They have been found quite far north but are only real pests south of Augusta or so. They are bothering some crops at MOFGA's site in Unity. Controls.

I often use Japanese beetles as an example of the few pests for which the organic approach has poor results. On turf, controls normally target young grubs just as they begin to emerge from eggs. In vegetables, managing the grub stage may not be feasible since the grubs are most likely feeding elsewhere and the adults are such good fliers even if you control the grubs in your own or nearby turf other adults will find you. Adult beetles normally do not cause economic damage except on the favorite crops I mentioned above and on flowers. Rotenone and Concentrated formulations of pyrethrum are options for controlling adults, but since they are such good fliers new ones fly in to replace the ones you killed. Personally, I think the damage done to the rest of the insects (beneficial or harmless ones) out weighs any benefits of spraying these. If you insist because otherwise you will not have any harvest, insecticides should be applied in the very early morning.

If there is concern about grub populations in cropped fields, such as new fields being prepared from sod, it may be possible to reduce grub survival through starvation (i.e., no crop roots to feed on in late summer, where that is possible). The tillage used to incorporate crop residues after harvest will bring grubs to the surface and expose them to predators. This needs to be done before November, when grubs move down deep for overwintering.

Another possibility is predatory nematodes. The best option would be Heterorhabditis bacteriophora, which can be purchased from insectaries and applied through a backpack or low-pressure boom sprayer as a soil drench. (Do not use Steinernema spp, which are ineffective against grubs.) The rate used on turf is 1 billion per acre but it could be less on bare soil because they are not lost in the thatch as in turf. They have to be watered in to get them down into the moist areas of the soil. Research studies conducted at UMass and elsewhere, using this species, showed quite consistent results (60-70% mortality) against grubs in turf. Traps baited with attractant may be another option for reducing Japanese beetle numbers, but care should be taken to place traps a distance away from any crop that could be damaged (preferably upwind). Studies out of Kentucky indicate that trapping of Japanese beetles results in increased grub activity within 10 meters of the trap. So placement would be crucial. As heavy as our beetle populations tend to be, trapping may not make a big dent. I have jokingly suggested that you give the traps to all your neighbors as gifts.

Modified from a report by Pat Vittum & Ruth Hazzard

VERTICILLIUM WILT

POTATO

Potato Late Blight has been found in Northern Aroostook and northern Central Aroostook County. Both late blight finds are small isolated areas. Late blight has also been found in a home garden in the Farmington area of Franklin County. The threat potential with the frequent shower activity is high. All growers throughout the state are strongly encouraged to be carefully scouting for this disease. Growers throughout the state should also be monitoring the potato leafhopper populations in their fields. Potato leafhoppers have been in the state for several weeks and leafhopper nymphs are now being found through our scouting area and populations are starting to build.

Aphids:

Winged green peach aphids were found in several fields this week. Most treated fields that we have scouted have had minimal or no aphid activity, however, untreated fields are reporting an increase in aphid activity. Wingless green peach aphids and wingless potato aphids are being found at levels exceeding the economic threshold in several untreated fields. Seed growers should be actively scouting fields for aphids at this time.

As seed growers prepare for vine killing please remember that aphid populations need to be managed until the vines are completely dead in order to reduce virus spread.

European corn Borer:

We are continuing to monitor ECB activity with our pheromone traps. Minor moth activity is taking place at this time. Our scouts have found some larval feeding in several fields. At this time the larval feeding activity that we have seen appears to be rather minor.

Colorado Potato Beetles:

A few fields within our scouting range are reporting some increased CPB activity at this time.

Potato Leaf Hoppers:

Potato leafhopper nymphs have been found in fields in Central Maine and Aroostook County at levels that have exceeded economic threshold levels. Leafhopper nymphs are capable of causing economic yield losses. The cool weather being forecasted for the next few days may slow development, however, all growers in the state are encouraged to be scouting their potato fields for leafhopper nymphs.

Recommended economic threshold: 10 nymphs per 100 leaves surveyed

SWEET CORN

(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.)