Hot weather, scouting for soybean disease

Tony Nye - OSU Extension

According to Jim Noel of the National Weather Service, the weather we have had thus far has included a few hot bursts this summer — but nothing like the stretch ahead.

So far May and June have been warmer and wetter than normal in most places. It looks like after showers in the middle of this week the weather will turn hot for the end of June and will last into the first half of July before relaxing some for the second half of July.

There may a day or two break from time to time during the warm weather the next few weeks but above normal temperatures will rule into July.

Rainfall also looks to relax more toward the normal range, but with longer stretches of dryness mixed in with the wetness.

According to Noel, the outlook for the first week of July calls for temperatures to average 6-8 degrees above normal with highs mostly 85-95. Lows will be 65-75. Rainfall will average 0.25 to 1.00 inches which again is normal to below normal for most of Ohio.

The outlook for the rest of July (weeks 2-4) calls for temperatures 1-3 degrees above normal and rainfall of 1-4 inches. Normal highs in Ohio are 80-85 and normal lows are 60-65. Rainfall normally average near 1 inch per week.

Looking further ahead in the growing season and harvest season, it appears August will still see slightly above normal temperatures and slightly below normal rainfall. September looks near normal temperatures and normal or slightly wetter than normal.

Finally, October appears to be about normal temperatures and slightly drier than normal.

Just remember it is Ohio and the weather can change. Based on what we have experienced thus far, I would not expect much different from what we have had so far.

So with that said, keep the AC running and hope we get timely rains throughout the rest of the season.

If you remember last week I mentioned to begin scouting crops, especially soybeans.

This week Anne Dorrance, Ohio State University plant pathologist, reported they received last week into the lab samples of frogeye leaf spot of soybean. On the underside of the characteristic lesion were the conidia. This came from an area where the incidence of frogeye was notable at the end of the season.

For the 2018 season a susceptible variety was planted back into that same field. Environmental conditions have been favorable for this disease to begin in some areas of the state.

However, most of the varieties in the state have very good levels of resistance to this disease and if good rotation is practiced it will take more time for enough inoculum to build up to begin to move around the state.

She notes there are numerous fungicides available for this foliar pathogen and in Ohio, but the caution here is the strobilurins.

Based on sampling over the past 3 years, the samples of this fungus in 2017 (last year) indicated that most of the populations were now resistant to the strobilurin based fungicides. Dorrance and others will begin testing any samples received this year in earnest, but based on last year’s sampling, farmers who are managing this disease should focus on using a triazole (FRAC Group 3) or a MBC Thiophanate (FRAC Group 1, thiophanate methyl) at the higher rates if disease is active in the field.

The best timing is one spray at R3, at the end of flowering.

This fungus will only infect young newly expanding leaves, so the goal in the spraying is to protect those big flushes of leaves as our indeterminant soybeans really fill out. Fungicide coverage should focus on the upper third of the canopy for this disease.

Dorrance reminds producers to be on the lookout for other soybean diseases that may be developing.

Early and mid-season Phytophthora. With each of these saturating rains, soybeans that have low levels of partial resistance, (tolerance) will continue to develop Phytophthora stem rot.

At this point, the plant should be able to hold its own against this pathogen if the resistance package is there. Make notes if it is not and choose a variety with better resistance scores for 2019.

White mold caused by Sclerotinia stem rot. Cool nights and random rains to keep the moisture levels up are perfect for this disease of soybean.

However, only in historically infested fields and only if the canopy is closed at those first flowers and most often on highly susceptible cultivars.

So double check your variety ratings that got planted in those areas with a history of white mold.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for 30 years, currently serving Clinton County and the Miami Valley EERA.

Tony Nye

OSU Extension