This newsletter and the advice herein are free. You usually get what you pay for.
A print-friendly version of this newsletter is available to download here: SW MN IPM STUFF 2019-7
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 SWROC Weather.
Early-planted corn is 7 collars here. In fields planted earlier than the SWROC, rows have closed. However, there are some corn fields that are much smaller.
Damage can happen quickly when larger larvae start to move from grass weeds or field edges to crops. Worth paying attention to these.
European corn borer (ECB)
Blacklight trap captures of ECB moths remain very low. 1st generation moths are still present at the SWROC where the current season total of five moths is running ahead of recent years. To put things into perspective, before the mid-1990s, when corn borer pressure was high, single night captures of 100 or more 1st generation moths were not unusual.
There is a limited number of light traps covering the state, so low numbers do not mean non-Bt corn is risk free. Based on degree-days, scouting for the 1st generation multi-voltine corn borer flight should be underway in the MN River Valley and SC MN. Based on recent moth captures, we may need to scout a bit longer than typical. ECB degree-day development models can be found at ECB degree-day model.
The wide range in corn planting dates will concentrate 1st generation egg laying in taller corn.
Remember, at this time, focus on non-Bt hybrids and don’t waste time scouting 1st generation ECB in corn less than 15-inch extended leaf height.
Similar to corn, soybean stages are extremely variable. The largest soybeans at the SWROC are V5. Other than a few small experimental and demonstration plots, most are much smaller. While I have not yet seen blooms, I suspect that some early planted fields have started. Read herbicide labels.
Those darn soybean gall midge
Only one of our study sites produced adults (Soybean gall midge adults captured in MN). In spite of the low number of adults captured, my research team found gall midge injury symptoms, and presumed larvae, in lower soybean stems from Rock County today. I was hoping we would not. Third instar larvae are orange while early instar larvae, like these, are white.
Someone forgot to bring the good camera, so I only have cell phone pictures to share. I’ll try to get some better visuals and try to set up a scouting clinic next week.
This spring, migrant painted lady butterflies keyed in on early-emerging soybeans. In areas where these fields were few and far between, egg laying and subsequent soybean damage was concentrated. Even in early emerging soybeans, growth was slow this spring.
Smaller soybean plants, fewer soybean leaves and, in some cases, thistle caterpillar behavior, can effectively increase the leaf area by a larvae. Thistle caterpillars and soybeans injured by herbicide can be a bad combination. Delayed leaf development and new trifoliates that do not unfurl and expand properly reduce the soybean leaf area available for caterpillars to feed on. Without new leaf development, caterpillars cannot create their shelters of silk tied leaflets. This may encourage the movement of hungry, homeless caterpillars to new plants.
Although thistle caterpillars will feed on giant ragweed, they apparently have expensive tastes. Soybeans were more frequently infested than ragweed in a SC MN field I visited this week.
Butterflies from these early-infested fields should start appearing within two weeks, and more butterflies have been seen arriving from the south recently. It is likely that we will see numerous painted butterflies in July. With many of this year’s soybeans fields delayed in development, 2nd generation thistle caterpillar infestations should be watched.
Nick Pieske’s Murray County pheromone trap captured a very large number of moths this spring. They must have laid a few eggs somewhere and Nick recently where found a couple spots where they had. Larvae had caused economic damage to a field of soybeans. Typically, unworked soybean residue is considered more attractive than corn residue to egg-laying black cutworm moths. I’ve had a couple reports of soybean damage where corn was drowned out in 2018. He also provided photographic evidence of damage to corn planted into manured alfalfa; a situation where I would usually suspect dingy cutworm. In both examples, infestations may have been related to early season weeds. Oh well... the black cutworm factsheet needed a few other edits anyhow.
It would be wise to get an initial look at soybean aphid populations around July 4th. At the SWROC, aphid populations are behaving similar to 2018 and struggling from late soybean emergence and wet weather. This past week, soybean aphids were also spotted at the Rosemount ROC by Bob Koch’s entomology crew. ”Deep throat” reported aphids in an early-planted Waseca County field. There are at least a few out there.
Aphids are most likely to be found in the earliest emerging soybeans now. Later in the season, winged aphids will seek out later maturing fields. The large number of very late planted soybean acres in some areas may make for an interesting August.
Potato leafhopper needs scouting attention during third cutting. Leafhopper adults are very mobile and will move from cut alfalfa to nearby soybeans and other hosts. New seeding alfalfa and dry beans are particularly susceptible to injury from potato leafhopper feeding while soybeans are much more tolerant. Curt Burns mentioned high leafhopper populations and hopperburn in some dry bean fields.
As I drive through southern and west central Minnesota, I am starting to see heading in some spring wheat and oat fields. As wheat nears flowering, look at Fusarium head blight and other disease forecasts at: Scab Epidemic Risk Model.
This could be a good year for bacterial streak in southern MN… or a bad year, depending on your perspective.
Scout armyworm in small grains, pay close attention to any lodged crop and adjacent grassy areas.