Appling County Crop E News

Disease Update June 5, 2017

Southern rust has finally been identified in Georgia in Seminole county. This is likely some of the earliest southern rust to affect our state.

Weather condition for the past few days and over the next few days is predicted to have a significant chance of rain and humid conditions. These conditions are quite favorable for the development and spread of rust diseases to include southern corn rust and Asian soybean rust.

Asian soybean rust has also been found on kudzu in Miller County and on corn in Seminole County.

UGA and Dr. Kemerait recommendations: Corn in southern Georgia that is approaching tassel stage (or has reached) is now at some risk to southern corn rust. The risk is likely not urgent yet, but finding rust now (fairly early in the season) and coupled with the current weather conditions does increase risk.

Growers spraying for southern corn rust: tebuconazole is effective, but combination products that include multiple modes of action (e.g. strobilurins, triazoles, SDHIs) have a broader spectrum of activity against disease AND have a longer protective window (e.g., 3 weeks versus 2 weeks.)

Peanut

Conditions are becoming more favorable for white mold now. There have been numerous reports of Aspergillus crown rot across the state, typically on very sandy and dry fields and often where farmer-saved-seed was planted.

As we approach the 30 to 45 day mark for a lot of peanuts, fungicides are on the mind of most growers. There are a lot of options available and deciding what to use, as well as, when to use can be confusing.

Options are good and having more available fungicides with newer strategies can better control disease. However, having lots of options can also be frustrating to decide what is best. Sometimes early applications can increase input cost while not always increasing yield.

During the first 30 days of a peanut the immediate threat from disease is generally lower than it is later on. That certainly doesn’t mean that peanuts are without disease pressure for the first 30 to 45 days. As mentioned above, Aspergillus crown rot has already been severe in some fields in parts of Georgia. Typically though, 30 to 45 days after planting is when fungicide sprays begin and a good foundation is laid for leaf spot control. More recently, this is also when the most aggressive white mold control programs begin.

Here are some opportunities and fungicide options following planting and through the first six weeks of the season:

  1. 30 and 44 days after planting remain important dates for establishing a good leaf spot program. These applications generally insure that the crop is protected before any significant infection by leaf spot pathogens has occurred.
  2. Years ago, most growers were using only chlorothalonil for the first spray; today there are an increased number of options.
  3. On well-rotated fields and/or where a more-leaf-spot-resistant variety is planted, use of chlorothalonil is likely appropriate and economical. However, where risk to leaf spot is increased (as measured using Peanut Rx), or for increased insurance, it often becomes important to be more aggressive with a leaf spot program. More aggressive leaf spot programs include fungicides early in the season with greater systemic activity (chlorothalonil is only a protectant).
  4. Use A fungicide like Priaxor (6 fl oz/A) at 45 days after planting and set the base for a strong leaf spot program with only one fungicide application in the first six weeks after planting.

The most important changes in our early season fungicide programs over the past decade have been to include control measures for soil borne diseases, particularly for white mold. Historically in Georgia, peanut farmers waited until approximately 60 days after planting to apply fungicides, like Folicur and Abound, to protect their crop from white mold and Rhizoctonia limb rot. Today, many growers are beginning their white mold program earlier. Though the “60 days after planting” timing remains the backbone of the white mold program, there are three reasons why growers may take steps to protect their crop earlier. First, research in recent years has shown that white mold can become established earlier in the season, sometimes well before a significant foliar canopy is established. While this may not normally occur, especially in well-rotated field, it does occur more often when the early season is unusually warm. Second, we now have fungicides, like Proline and Elatus, which are marketed for and proven to be effective in management of early-season white mold situations. Last, tebuconazole is so inexpensive these days that many growers see that including it with early-season leaf spot applications does not increase cost and may help in establishing the most robust white mold program.

Here are a few more suggestions for deciding the best spray program:

First, don’t be late. Timeliness is a key factor in the success of any disease management program. Based on Peanut Rx and disease risk, not all programs need to start at 30 days after planting, but it is important to know when to start. It is hard to play “catch-up” with diseases.

Second, use Peanut Rx to determine risk- risk based on all factors to include variety, rotation and planting date. In higher risk fields, don’t be afraid to spend money on a more effective program, if it is needed.

Last, growers SHOULD NOT feel pressured to use the most expensive program, to include number of applications and timings of applications, if the disease risk does not justify it. A good fungicide program is a good insurance policy. However, over-spending on that policy with very little chance of a positive return may not be the best use of your money.

 Contributors: Dr. Bob Kemerait