SW MN IPM STUFF 2017 Issue 3

05/19/2017

This newsletter is also available in a print-friendly pdf format: SW MN IPM Stuff 2017-03

This newsletter and the advice herein are free. You usually get what you pay for.

Crop Weather

Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University of Minnesota Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN, can be found at http://swroc.cfans.umn.edu/weather.

Minnesota rainfall map from May 11-18, 2017

Figure 1. Rainfall May 11-18. May continues to be wet in many areas. This spring’s weather patterns will influence insect and diseases of MN crops, as well as overall yield.

The wet weather continues with more in the forecast. In areas with heavier rain, there is some ponded water. Provided that fields drain relatively soon, cool weather will aid crop survival and the need for replants minimal. Soybeans are beginning to emerge in early-planted fields. For the most part, emerged corn stands look good from the road but they need closer attention than a windshield survey once it dries out a bit.

There is a shear layer below spring tillage depth in fields with clay loam soils that were worked a bit early. This layer, along with any issues created last fall, has the potential to cause issues as roots develop.

Root problems associated with seed depth, seed to soil contact, crop nutrients and compaction will start to show up once corn needs to rely on nodal roots. Some seedling root diseases and insect injury present similar symptoms.

Corn growth and soybean emergence will be slowed with the cool weather in the forecast. Seed and seedling damaging insects (seedcorn maggot, wireworm, white grub) sometimes cause more problems with slow emergence. Fortunately, economic problems from these insects have been relatively predictable and rare, even before neonicitinoid seed treatments were available. Prolonged, water saturated conditions favor many seed and root infecting pathogens. Treated seed or not, scout your stands.

alfalfa weevil adultFigure 2. Alfalfa weevil adult on sweep net fabric.

Alfalfa

Alfalfa weevil adults, 1st instar nymphs, and undoubtedly eggs, are present in southern Minnesota 1st cutting alfalfa.

Low populations of pea aphids and tarnished plant bugs are present as well. I have not yet picked up potato leafhopper in alfalfa sweeps but migration into other fields and areas might be different. Sweep nets are very helpful.

Cereal Grains

Immigrant aster leafhopper adults have become abundant in some but not all winter rye plantings at the SWROC. Aster leafhopper can transmit a phytoplasma that causes the disease aster yellows that affects many broadleaf ornamentals, vegetable crops and potentially wheat. Leafhopper populations, while higher than average are not near the epic levels we saw in 2012.

Crown rust aescia are present on buckthorn leaves. I have observed rye leaf rust on winter rye but as of yet no wheat leaf or stripe rust on winter or spring wheat. I expect that to change soon.

When checking winter rye and winter wheat plantings at the SWROC, thrips were very abundant, much higher populations than I can remember seeing before. My skills at identifying thrips to species is very weak but I believe these are a flower thrips. These long-bodied insects are tiny, less than 1/16-inch long. The immature and adults are yellow to orange in color. The adult’s four wings can be seen with magnification to have feathery hairs at the edges. They have a wide host range.

silvering wheat leaf

Figure 2. The silvering on this wheat leaf was caused by the feeding of thrips. The black dots are thrips frass (feces). There are also numerous orange pustules of wheat stripe on this 2008 leaf.

Soybean thrips are similar in size and shape but have a distinctive light and dark horizontal banding. The dark colored, barley thrips can be an economic pest of cereal crops. Both of these are present in Minnesota crops.

The mandibles of thrips mouthparts are asymmetrical. In the species that feed on plants, the left mandible is used to scrape the epidermous of plant cells from which the thrips suck sap. These injured cells collapse; creating a very distinctive silvery scarring.

Other plant feeding thrips species create galls, and still other thrips species are predators. While flower thrips are not known to have a taste for human flesh, they will bite people just to make sure they are not edible. I have frustrated quite a few thrips this spring. 

While feeding on plants, thrips can transmit virus diseases. Some of these include tobacco ringspot, tomato spotted wilt, and soybean vein necrosis. The cool, wet weather might work to our advantage and we will have to see if these insects create any problems.

Things that go bump in the night

Summer intern with insects

Figure 3. Summer intern Matt Wordes after sorting through the bucket of bugs and other insects captured in the SWROC light trap.

All of the MN insect black light traps are not yet on line for 2017. Based on the limited number of traps reporting at this time, true armyworm moths are present but at low levels. This may change after the recent rainfall events pulled Gulf moisture, migrating insects and perhaps wheat rust spores from the south.

Cool weather has slowed moth and other insect activity many nights. By far the most common night flying insects now are several species of mosquito–like Chironomid midges. At the SWROC, two species of May beetles are now emerging and showing up at lights.

European corn borer flights in southern Minnesota are still 1½ to 2 weeks away. You will be able to track 2017 corn borer and Corn earworm flights at the University of Minnesota VegEdge site https://www.vegedge.umn.edu/moth-data during the growing season.

Black cutworms from the earliest significant migrant flights should be feeding on leaves now. Feeding injury may be as limited as small pinholes. Black cutworm larvae will be too small to cut plants until the end of May. However, other overwintering cutworm species may be larger and able to cut earlier. Weekly black cutworm captures are available at MN black cutworm reporting network. See the most recent issue for projections of when cutting will occur.

Recently updated Black cutworm information on black cutworm biology and management is available at this same site.

There are challenges to running these insect trap networks. A momentary loss of concentration and you find your head glued to an insect pheromone trap. Then there’s always those who want to take advantage of your work. This spring, one of the black light operators had a problem with a couple starlings that insisted on building a nest in the bucket of his trap, presumably for the easy access to an insect food source. [The birds] “Just sit there, the bugs come like mana from heaven. We kept cleaning it out but they were back. We could not catch them until yesterday when they were wet and could not fly...not a problem anymore.”

Pyrethroid comment period re-opened

Pyrethroid insecticides are under EPA review, the public period has been reopened until July 7th see: https://www.regulations.gov/document?D=EPA-HQ-OPP-2010-0384-0092.

Soybean aphid watch 2017

Warm, wet weather means any soybeans that did not make it out of the field should have germinated last fall. There was also a large percentage of aphid mortality from fungal diseases late last summer and parasitoid wasps seem to be more in recent years.

Particularly in portions of southern Minnesota, the cold, wet spring weather is not likely to favor soybean aphid populations on buckthorn this spring and has slightly delayed soybean planting and emergence relative to buckthorn.

While this is reason for a bit of optimism, I do not know if this is enough to greatly reduce early season colonization success. There are plenty of areas for 2017 soybean aphid populations to become established. Stay tuned.

-Bruce Potter