Pest and Disease Update June 18, 1999
CROP CONDITIONS
PESTS:
POTATOES
STRAWBERRIES
CORN
CUCURBITS
CRUCIFERS
Hello again,
Remember, we have a lot of people to thank for information in this message;
Ruth Hazzard and Sonia Schoelmann from the UMass Extension, Clay Kirby, Dave Handley and Jim Dwyer from UMaine Extension, Vern Grubinger from VT Extension, and MOFGA growers. Please send me any interesting observations from your farms and I will spread the word.
It is still very dry over most of the state. The crops that are in a sandy soil with no irrigation are growing very slowly and may show N defeciency. Those with water are doing very well with abundant sun shine, dry weather and plenty of heat for this time of year. Everything is a week or more ahead of schedule.
I saw silking corn this morning on my way to the office...started under plastic no doubt. Strawberry picking is in full swing in central Maine and it looks like it will be a very good year for those who did not lose it all to the frosts in late May. Haying is going quite well. Disease pressure is low thanks to lack of water.
I have heard reports of potato leafhopper in Mass, be on the look out. We often start to notice injury during early and mid summer, especially in new strawberry plantings, potatoes, and beans. These insects don’t overwinter in Maine but fly in every year from more southern states. Usually they come in low numbers but sometimes it is bad. When it is bad it is real bad. Adults and nymphs feed by inserting a needle-like beak into the plant and sucking out sap. They also inject a toxin into the plant, which causes yellowing, browning, and curling of leaves. Plant injury and yield loss can be significant. Pyrethrum sprays work if you catch the pest early. Look for the wedge shaped adults by brushing the crop with your hand and looking for a small cloud. The nymphs are small and cannot fly. They are easily identified by their habit of walking sideways when disturbed.
OTHER PESTS
Garden springtails have been reported down east to be bad. The damage from these pests is similar to flea beetle damage and similar to flea beetle the plants usually out grow it. It is usually only a problem in the spring. They are funny looking critters with an appendage between their legs that when it springs off they go. If you are not sure if the pitting in you early beans, etc is from flea beetle or springtails, try putting out white sticky traps at ground level. Control of very bad infestations is with a 5% rotenone dusting.
Earwigs are usually not a real problem, but I have heard a report of potatoes being made into lace. You have to check at night to find the pest feeding. If you have a real problem, get in touch with me and I will send plans for traps.
Cutworms are big and still active.
I have heard a report of the golden tortise beetle devouring tomatoes. The beetle has its head hidden under the front of its thorax, hence its name.
Adult potato beetles are active now and laying eggs. Be sure to monitor your fields carefully because if the young larvae are not controlled now, they will be much more difficult to control when the get larger. Flag about 10 egg clusters and watch for hatching. When most have hatched, spray with Novador or equivalent Bt product. Spray again about a week later. I have seen great control with just two sprays a season if the timing is good.
Jim Dwyer reports that as of last week, some of their late blight forecasting stations have reached or exceeded the 18 severity value threshold for potato late blight. This means that it is possible for potato late blight to become active, if present, within the next 10-14 days, if conditions are suitable for disease development. Cool, moist, and humid conditions are the ideal situation for disease development. Growers are strongly encouraged to have protective fungicide sprays (copper based fungicides such as Champ or Kocide) on prior to the next infection period.
I hear that the European corn borer is a great concern this year. We have a grower who has set up traps in the county and will keep us up to date. For the central part of the state I will forward the info from the corn hot line. (If you would like to call yourself, the number is 933 4647).
There has not been any gray mold yet because the fields are very dry, but the potential is there. Remember, the initial infection of the crop takes place during bloom when the sepals of the flowers are infected by spores from overwintering mold in your fields. Since we did have some wet periods during bloom it is likely that there is plenty of infection in the field that will take off if the conditions turn wet.
The clipper and tarnished plant bugs are not a real threat anymore. Two spider mite are a threat and numbers may rise in hot, humid weather. Mites are usually not a problem in organic fields where the predatory mites in residence are not killed by sprays. But you should monitor and release store bought predatory mites if your in house ones cannot keep up with the TSM.
The European corn borer is active now around the state and laying eggs. The first eggs are layed on the underside of the leaves and the larvae crawl into the whorl at this time of year. Feeding damage is noticed as the leaves grow...the leaves that have been fed on in the whorle come out with small holes all over, like shot gun holes. There is little feeding damage noted yet. Look for damage in your own fields by sampling 100 plants in a X pattern in the field. If damage is noted on more than 30% of the sampled plants in the whorle stage, or 15% of the plants in the pretassel stage it is time to spray a Bt product. Condor has worked very well. When corn is in the silk stage eggs can be layed there and the borer goes right into the ear. Of course, you do not see any damage this way and scouting does not work. If you see a lot of damage in the younger corn, then spray any corn in fresh silk stage.
There have been the first catches of corn earworm in southern Maine. These are very early and are not likely to be a real infestation, and are not a concern because there is very little silking corn now. More on this pest next time.
Pumpkins and squash are growing fast, as long as they have even moderately adequate water. Striped cucumber beetle numbers were very low this week. Even newly-emerged plantings had few beetles and very minimal damage. Some restocked fields had minor feeding on the new cotyledons. Pumpkin and winter squash plants reaching the 4-5-leaf stage are out of danger. Aphids were observed in one field last week, but numbers declined between scouting visits.
Weed control is the major concern as plants approach the vining stage. Cultivations should be shallow, and the last cultivation should be timed to clean up weeds just before vines run.
Watch for imported cabbageworm in cricifers. If you see the white moth flying around it is time to get the Bt ready. Spray when you see the small larvae feeding on the crucifers. Cabbage looper moths were captured in pheromone traps again this week in Mass.
(About the author: Eric is MOFGA’s "extension agent" and can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)