ISSUE 14 August 16, 2007
CONTINUE MONITORING FOR SUNFLOWER MOTHS AND OTHER HEAD INSECTS IN LATE BLOOMING SUNFLOWER FIELDS
Continue monitoring for sunflower head insects (banded sunflower moth, red sunflower seed weevil and sunflower moth). Recent field reports indicate high populations of the sunflower moth in southern tier of North Dakota. In some cases, fields were heavily infested destroying the entire sunflower head, up to 30 larvae per head near Mott! There’s been a few reports of sunflower moth found further north into McKenzie County. Banded sunflower moth traps have finally started to decrease last week and egg laying should be minimal. Red sunflower seed weevil are still active and will be attracted to sunflower fields in the flowering R5.1-R5.7 stage. After R5.7, the sunflower seed becomes too hard for egg laying and is no longer attractive to the red sunflower seed weevil. Scout fields to determine what your population level is. See previous issues of Crop & Pest Report in 2007 for scouting tips and thresholds:
Sunflower moth - Issue 13, August 2
Banded sunflower moth - Issue 12, July 26
Red sunflower seed weevil - Issue 10-12, July 12-26
LATE SEASON SOYBEAN INSECT UPDATE:
Scouting should focus on the late planted soybean fields.
Bean leaf beetle has been making an appearance by creating circular holes in the leaves (see photo) and clipping some pods in the southeastern region of North Dakota. Bean leaf beetles vary in color from yellow to reddish-brown, and may have three to four black spots with a black border on the wing covers (see photo). Adults emerge from overwintering and move into newly emerging seedlings. Larvae feed on the roots and nodules in the soil. New adults emerging in August feed and foliage and pods. The feeding lesions on pods serves as secondary infestations by fungi and bacteria, causing rotting and discoloration. For a treatment threshold in mature soybeans, use 20% defoliation in the pod-forming and pod-filling stages; or 10% pod feeding or the presence of clipped pods. As it gets closer to harvest, consider the preharvest intervals when selecting your insecticide.
Bean leaf beetle (photo by N. Wright, Fla. Dept. of Ag.)
Bean leaf beetle injury
Soybean aphids continue to be at low levels and soybean development is getting closer to the R5 (beginning seed) and R6 (full seed) stage. So, it looks like most areas of North Dakota will escape the need for any insecticide treatment for control of soybean aphid.
Good news for most soybean producers! The economic injury level increases as the crop stage matures; however, research is still continuing on what the exact threshold is. At R5, we still recommend using the 250 aphids per plant threshold and increasing populations; however, the probability of getting a positive yield response is less predictable. At R6, a nominal threshold of 1000 aphids per plant is recommended.
Low levels of foliage feeding caterpillars are being reported on soybeans, including green cloverworm, cabbage looper and velvetbean caterpillar. Typically, these caterpillar occur sporadically and cause little or no damage to soybean in North Dakota.
Green cloverworm: These caterpillars are green with two narrow, white stripes down the side. When mature, the worms are 1 ¼ inches long. These caterpillars have only three pairs of fleshy prolegs on the abdomen, plus a pair of prolegs on the back segment. When moving, the worms move by arching the middle of the body, or "looping." Young worms scrape leaf tissue creating a transparent skin, or "window," on the leaf surface. Older cloverworms eat holes in the leaves.
Green cloverworm larva (photo from Clemson Univ.)
Cabbage looper: These caterpillars are light to dark green, with lighter colored stripes along the side and on the top, running the length of the body. When mature, the worms are 1 ½ inches long. These caterpillars have only two pairs of fleshy prolegs on the abdomen, plus the pair on the back tip. When moving, the caterpillars move by arching the middle of the body, or "looping." These worms feed on leaves in the interior and lower portion of the plant. As defoliation occurs, worms feed higher in the plant. Feeding injury is similar to the cloverworm.
Cabbage looper larva (photo by D. Cappaert, MSU)
Velvetbean caterpillar: This insect does not overwinter in the region; instead, moths migrate from Southern locations. These caterpillars have dark lines bordered by lighter colored, narrower lines running the length of the body. The background color ranges from a pale yellow-green to brown or black. These larvae have four pairs of fleshy prolegs to distinguish them from the cloverworm and the looper. Young velvetbean caterpillars feed on the underside of leaves in the upper portion of the plant. Older larvae consume the entire leaf, except for the leaf veins.
Velvetbean caterpillar (photo from Clemson Univ.)
Threshold: Rather than using a threshold for each individual defoliating insect species present in the field consider total leaf area losts as a theshold. When defoliators are actively feeding: vegetative = 40% defoliation, pre-bloom = 30%, bloom = 20%, pod fill = 15%, and post-pod fill to harvest = 30%. The threshold usually requires an average infestation of 4 to 8 larvae per row foot.
PREVENT STORAGE INSECT INFESTATIONS IN THE BIN
If it continues to stay warm this fall, it may be another busy season for the grain storage insects as they infest your bins! So, take some time now to prepare your storage bins and prevent potential stored insect problems through good bin management. There are several good reasons to prevent insect problems in the bin. One, most countries have a zero tolerance policy for insects in grain destined for export. And two, practices to prevent insect infestation of stored grain are relatively simple and cost a lot less than practices commonly used to protect a growing crop from insect losses. Several species of insect infest stored grains in North Dakota: confused flour beetle, Indian meal moth, rice weevil, lesser grain borer, red flour beetle. Damage caused by these insects includes reduced grain weight and nutritional value, contamination, odor, mold, and heat damage, which lowers the grain quality.
Good grain bin management practices include:
1) The first step is to make sure that the bins are clean and free of insect-infested grain. Left over grain should be removed from the bin, and the walls should be swept and vacuumed. All grain handling equipment including augers, combines, trucks and wagons should be thoroughly cleaned and grain residues removed before harvest. A residual bin spray such as malathion, tempo, or Storcide II should be applied to all interior bin surface areas 2 to 3 weeks before new grain is placed in the bin. The treatment will kill insects emerging from their hiding places (cracks, crevices, under floors and in aeration systems). Also, insects crawling or flying in from the outside will be killed.
2) When cleaning the bins, remember to get under aeration floors and inside aeration tubes. These are great spots for insects to hang out while waiting for you to fill the bin again.
3) Remove any vegetation / weeds that may attract and harbor insect pests within 10 ft of a bin and preferably the whole storage area. Follow by spraying the cleaned area around the bin with a residual herbicide to remove all undesirable weedy plants.
4) Repair and seal all damaged area to grain storage structures. This help prevent insect infestation and reduce water leakage which leads to mold growth.
5) Whenever fans are not operated, they should be covered and sealed to reduce the opportunity for insects and vertebrates to enter the bin through the aeration system.
6) If newly harvested grain and/or insect-free grain must be added to grain already in storage, the latter should be fumigated to prevent insect infestation.
7) If grain will be in storage for one or more years, it is recommended that grain be treated with an approved insecticide as it is augured into the bin. Grain protectants kill insects as they crawl about or feed on treated grain and/or grain fragments. Do not apply grain protectants before high temperature drying because extreme heat will result in rapid volatilization and reduced residual qualities of the pesticides. Grain protectants applied to 13% moisture grain will have a greater residual life than grain at 15% or great moisture. Moist grain is also more attractive to insect infestations. Canadian research has discovered that ‘pea flour extract’ has some natural repellent properties and insecticidal activity against stored grain insects. Patents have been obtained for both U.S. and Canada for the extract process. Currently, the Agriculture and Agri-Food Canada is looking for a partner to commercialize the pea flour extract.
Please consult the 2007 Field Crop Insect Management Guide for a complete list of stored grain insecticides.
Another important step in preventing insect infestations is immediate cooling of the grain after harvest. Grain insects that are flying in the general area will be attracted to harvested grain by smell. They can find and infest grain on the truck or through an open grain bin hatch. If the grain in warm, above 50 F, they will start feeding and reproducing immediately. When temperatures are above 50 F, bins should be inspected for insect activity every two weeks. Stored grain insect pests are generally inactive at temperatures below 50 F (see diagram).
The final step in prevention of insect problems is regular inspections of stored grain. Use a grain probe to determine what species of insect pests are infesting the grain and the extent of infestation within the grain mass.