Alfalfa Weevil Scouting

May 27, 2020

By Bryan Jensen

Southern Wisconsin has reached the benchmark for alfalfa weevil scouting. Northern Wisconsin will probably hit the magical 300 DD total (base 480) within a week or two. Of course, that all depends on temperatures. Regardless, keep an eye out for weevil feeding on first crop alfalfa.

Alfalfa weevils are monitored by looking for feeding signs, often described as pin hole feeding. At the 300DD scouting threshold, those signs will in the upper developing leaflets and may be difficult to see with casual observations. At 300 DD weevil larvae are in the early stages of development and feeding holes will be small. You may have to unfold the upper leaves to find damage. As larvae grow the amount of defoliation increases substantially. Therefore, looking for early signs of feeding can give you a look into the future. In recent years, weevil feeding has been rather light. However, just about every year I hear of hotspots showing up somewhere.

Economic threshold for first crop alfalfa is to treat when 40% of stems have signs of weevil feeding and you are more than 1 week from harvest. If possible, plan to harvest heavily infested fields first. Double check regrowth to make sure larvae are not feeding on second crop regrowth.

This year the timing of first crop harvest and peak weevil feeding may not be what you typically expect. In a “normal” year, weevil feeding peaks about the same time as first crop harvest. This year the cooler temperature may change that crop/pest relationship. That is, alfalfa has a lower base development temperature than weevils. We may see peak weevil feeding later than normal when compared to crop development.

Source : wisc.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.