Small Grains Disease and Pest Update 07/10/23

Jul 11, 2023

The crop scouts continue to find grasshoppers and a few aphids here and there. The first white heads are starting to show in the earliest wheat fields. This means one of six things; Fusarium crown rot, common root rot, wheat stem maggot, wheat stem sawfly, Hessian fly, or Fusarium head blight.

The easiest way to tell what caused the premature death of these individual culms is to pull them up. Wheat stem maggot is the culprit if only the top node pulls out and the bottom of that node looks chewed on. Wheat stem sawfly is the culprit of the whole culm pulls up, it looks like the bottom of the culm was cut with a razor blade, and you find the hollow stem filled with, what looks like, sawdust. The damage was done by Hessian fly if you find one or more maggots that look like flax seeds.

If you pulled up the whole plant, the premature senescence was caused by either common root rot or Fusarium crown rot. In both cases, the vascular system in and around the crown was compromised by the fungal diseases and the root systems no longer could pump enough water to the above-ground parts.

Fusarium head blight is caused the premature senescence if the top portion of the peduncle (top internode) or part of the rachis has a bleached appearance.

The most likely causes at this point are the root rots, followed by wheat stem maggot. Wheat stem sawfly can be the culprit, especially if you are wheat on wheat. I'm unsure of how widespread the Hessian fly problem is.

I expect there to be little to no Fusarium head blight as the weather continues to be unfavorable for Fusarium head blight to develop.

This week's cooler weather forecast is good news for small grains' yield potential and will further reduce the risk for FHB.

Source : umn.edu

Video: Wheat Yields in USA and China Threatened by Heat Waves Breaking Enzymes

A new peer reviewed study looks at the generally unrecognized risk of heat waves surpassing the threshold for enzyme damage in wheat.

Most studies that look at crop failure in the main food growing regions (breadbaskets of the planet) look at temperatures and droughts in the historical records to assess present day risk. Since the climate system has changed, these historical based risk analysis studies underestimate the present-day risks.

What this new research study does is generate an ensemble of plausible scenarios for the present climate in terms of temperatures and precipitation, and looks at how many of these plausible scenarios exceed the enzyme-breaking temperature of 32.8 C for wheat, and exceed the high stress yield reducing temperature of 27.8 C for wheat. Also, the study considers the possibility of a compounded failure with heat waves in both regions simultaneously, this greatly reducing global wheat supply and causing severe shortages.

Results show that the likelihood (risk) of wheat crop failure with a one-in-hundred likelihood in 1981 has in today’s climate become increased by 16x in the USA winter wheat crop (to one-in-six) and by 6x in northeast China (to one-in-sixteen).

The risks determined in this new paper are much greater than that obtained in previous work that determines risk by analyzing historical climate patterns.

Clearly, since the climate system is rapidly changing, we cannot assume stationarity and calculate risk probabilities like we did traditionally before.

We are essentially on a new planet, with a new climate regime, and have to understand that everything is different now.