Rust watch continues
Jul 5, 2005 11:50 AM, By Alan Blaine
EDITOR’S NOTE: Conditions are changing rapidly in Mid-South soybean fields. Below is an updated version of Alan Blaine’s column which appears in the July 8, 2005, issue of Delta Farm Press.
Tropical storm Arlene brought rainfall to the eastern portion of Mississippi, closely following the path of last year’s hurricane Ivan. Predictive models have shown that the potential for movement of Asian rust spores was enhanced greatly.
We should have a better handle on the presence of rust if Arlene changed our current (June 23) scenario; however, the inoculum potential still appears to be low. Since Arlene, rust has been found in a sentinel plot in Baldwyn County, Ala. Although rust appears to be moving, the inoculum potential in Florida and Georgia has not increased at the rate most believed.
A large protion of the Mississippi crop has reached the stage when fungicides are usually applied. Rust is not the only problem we have in the south, so remember to look at the big picture: rust’s overwintering capability, stage of the crop, and future weather conditions.
I am not downplaying rust, I just want you to realize there are numerous considerations to take into account prior to deciding what to do. Many decisions will err on the side of caution, but understand what you are doing. Understand why you make a fungicide application and what it can do for you.
We have spent a lot of time planning fungicide trials centered around rust, but we may not have rust to deal with. However, we have enough potential problems that a well-timed fungicide program for other diseases can pay for an entire rust program. I hope rust will be minimal this year and our knowledge base will continue to increase.
Most of the Mississippi soybean crop went through extreme drought stress the first of June. Although the crop was young, we saw widescale plant death right after it rained over most of the state. We observed several diseases, but everything we identified was due to extremes in growing conditions.
Although plant death coincided with the rains, many of the plants were going to die anyway because they had gone too long without adequate moisture. You may disagree with that conclusion, but growers in our SMART program who watered prior to the early June rain did not have plants die.
This was proof we went a little too long without adequate moisture. Thin, droughty areas of fields suffered first. The earliest planted, most mature plants showed more stress due to the fact that they were in peak demand for moisture.
Insect pressure has been light, but a couple of unusual problems have surfaced: potate leafhopper (widespread) and spider mites. As was pointed out in a previous issue of Delta Farm Press, soil grubs have been observed fairly widespread. They appear to have increased the last couple of years (maybe because we are looking at the crop more) but are being found predominantly in no-till fields. Grasshoppers and threecornered alfalfa hoppers have been observed in greater numbers in no-till plantings.
As it has become drier, potato leafhopper damage has increased. Although the damage usually appears to be cosmetic, we have seen situations where spraying has allowed plants to resume growth. Leafhopper damage will be worse on varieties that have fewer leaf hairs, but this is not a characteristic we normally measure as in cotton.
Regardless of your crop situation, treat every field individually. The easiest decision is the decision to spray, regardless of the problem.
Alan Blaine is the Mississippi Extension soybean specialist. e-mail: ablaine@pss.msstate.edu
