Pest Report for July 25, 1999
Remember to thank all my sources for info if you run into them including Dave Handley and Jim Dwyer from U Maine Extension, Ruth Hazzard and Sonia Schoelmann from U Mass Extension, Vern Grubinger from Vermont Extension, Clay Kirby from the Pest Management Office and the MOFGA certified growers who take the time to send me reports from the field.
CROP CONDITIONS
TARNISH PLANT BUG ALERT!
POTATOES
SWEET CORN
EGGPLANT
PEPPER
Please send along anything interesting you note in your fields.I am getting fewer reports from the field recently. I bet that is because you all are busy harvesting and selling. And, by this time of year you think the crops have either made it or not. For the most part you are right, but don’t let your guard down and keep me informed of anything new.
Thanks
Most of the state got rain this past week, ranging from none to one and a half inchs . It helped, but much more is needed to alleviate the longterm effects of the drought. I got the inch and a half and my fields dried out again in two days! Reports are coming in of reduced ear quality in sweet corn fields in Mass. that have been dry too long. I suspect we will see the same in Maine. Succession crops are bunching up. I have four plantings of corn all silking at the same time. Even with drip oroverhead irrigation it can be difficult to keep up with crop’s water needs when the soil conditions are so dry and heat so intense. Not an easy year. But crop yield and quality are excellent where water has been sufficient!
The news from the County is slightly different. They have not been as dry as the rest of us. The 90 plus degree temperatures last weekend has produced some sun scald on foliage in many potato fields, but the shower activity has allowed plants to continue to grow nicely.
All growers should be carefully scouting fields at this point. Aphid populations are starting to build, potato leafhoppers have been found in increasing numbers, and Colorado potato beetle activity is also increasing. Insect activity has been extremely varied throughout our scouting range, which is why scouting is so important.
A REPEAT...TARNISHED PLANT BUG ALERT.
I am getting lots of reports of damage and I have a hard time to convince growers it is the TPB. Damage includes wilting growing tips and missing flowers in potatoes, no fruit in peppers and eggplants, brown florets in broccoli heads and more.
Tarnished plant bug, which feeds on many different plant hosts, is being reported in high numbers and could cause problems in crops where it would normally not be found. Adults are about 3/16 inch long with a shiny yellow to brown-black appearance and a distinctive triangular pattern on their backs. They move quickly when disturbed flying short distances. This pest feeds by sucking plant juices, and their saliva contains a toxin which kills cells near the feeding site. In strawberries this caused a lot of button berries this year. Now in vegetables this is causing distortion of the growth surrounding their "sting marks", yellow or brown spots, wilting of new growth, or abortion of flowers and fruit in fruiting crops. Injury may occur in celery, beans, lettuce, Chinese cabbage, broccoli, cauliflower, asparagus ferns, eggplant, pepper, potatoes, squash, and tomato fruit, as well as various cut flowers. Thresholds and control options vary depending on the crop—and in many cases, no thresholds exist since this in not normally a pest. Often tarnished plant bugs have moved on by the time the damage is observed. However, it may be worth keeping an eye out for high numbers of this pest. If things seem really bad Pyrenone works well to knock down the population, but new ones will be back since they feed on about 300 different kinds of weeds so are all over the place.
POTATOES Aphids:
Aphid populations are beginning to build and several fields this week have exceeded the recommended economic threshold for aphids. Our scouts are finding mostly potato and buckthorn aphids, but some wingless green peach aphids are being found. One field recorded 26% of the plants with wingless green peach aphids. Winged green peach aphids are also being found in very low numbers in some locations. Aphid population distribution patterns are totally random at this point and all growers, especially seed growers, need to be scouting fields for aphids.
Growers should also be aware that melon aphids have been found in one location in Central Aroostook. These will look like a dark colored buckthorn aphid-please contact your local Extension office for assistance in identification.
Colorado Potato Beetles:
Colorado potato beetle larvae activity is continuing to increase in many fields throughout our scouting range. Adults, large and small larvae are now being found in large numbers in some fields. The use of less than labeled rates of insecticide may save money in the short term, but will probably promote insecticide resistance and shorten the usable life of valuable products. Use Bt wisely. Do not try to kill every beetle. Later in the season potatoes can take a lot of defoliation and show no yield loss. Do not try to kill every beetle especially then.
Late Blight:
Only one isolated report of late blight has occurred as of this writing. All growers, however, should be carefully be scouting for this disease. The earlier that it is found, the more options that you, as the grower, have for control. Sun scald and botrytis are also being found in some fields, which can be confused with late blight. Plant samples can be brought to your local Extension office for identification.
European Corn Borer:
Moth activity at this point is rather minor. Plant damage caused by ECB escapes or untreated insects will appear as a wilting branch with a small entry hole visible. The corn borer larvae are very small at this time and can be easily confused with other stalk borers. Several other stalk borers, such as the potato stalk borer and the common stalk borer, are active at minor levels in our scouting range.
Potato Leafhopper:
Potato leafhoppers, both adults and nymphs, are now being found in the Central Maine area. This past week, several fields exceeded the recommended economic threshold for potato leafhopper nymphs, which is 10 nymphs per 100 leaves scouted. Leafhoppers are capable of causing significant damage. This situation should be watched carefully.
Corn harvest is getting into full swing in Maine. Native corn means native corn now. The dry fields are hurting lots of growth.
Corn Earworm
Moth captures continue to be quite low in most locations. Growers are maintaining a relaxed spray schedule or not spraying at all depending on trap counts. For example, a single spray was recommended in Cape Elizabeth, Dresden and Gorham, while no spray was needed in Auburn, Lewiston, Monmouth, Fairfield, and other locations.
European Corn Borer
Numbers of ECB moths caught in pheromone traps have fallen significantly in most locations. However, the IPM scouts have found numerous ECB pupae in corn stalks, indicating that there is a good chance for a second generation of moths to emerge and threaten corn before the end of the season. Larval feeding damage was over the 15% threshold in Wells, Wayne, Lisbon, Lewiston, Jefferson and Thomaston and a single spray was recommended for those fields. Scout your fields and use a Bt such as Condor if needed.
Fall armyworm
Moth captures in pheromone traps were generally much lower this week. No location exceeded the threshold of three or more moths per week in silking corn.
Deer have been bothersome in some fields of corn and squash. They chew off the tips of corn ears, and will devour squash vines. The latter are thought to be a source of moisture for these animals during this dry summer. Electric fencing is the most dependable solution to four-legged pests, and should be put up before they become accustomed to feeding in your fields.
In eggplant, watch for newly-emerging Colorado potato beetle adults, which can cause significant feeding damage to buds and flower petioles as well as leaves. Adults may need to be controlled to prevent damage. Bt will not control the adults. You will have to turn to rotenone or pyrethrum if it looks bad.
Also look for yellow egg masses under the leaves, and note new hatch of larvae. Bt products are effective only when when larvae are young.
Weather-related problems include blossom end rot and poor fruit set. Adequate and consistent water decreases the likelihood of blossom end rot. We are also seeing fields with a few large fruit then a gap in fruit set. New buds are plentiful but the current fruit load is light. Heat and drought may have induced poor fruit set or abortion of blossoms.
The onset of second-generation European corn borer flight—which is predicted this year—is a signal to begin a countdown to the time for the first insecticide applications for ECB control in pepper. When ECB moths captures exceed 7 moths per week on your farm or in your region, begin sprays one week later. Some locations reached that threshold this week in Mass.
Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.
(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.)