Foliar Fungicide Application For Early Disease Control

Cool conditions over the last 7-10 days have slowed the wheat down considerably, however, the development of the crop is still close to what is considered normal in Ohio at this time of year. Current growth stages range from Feekes 6, jointing, to Feekes 8, flag leaf emergence. At Feekes 6, the first node is visible at the base of the stem, about an inch or so above the soil line; at Feekes 7, two nodes are visible, one about 2 inches above the soil line and the other about 3-4 inches above the first; and at Feekes 8, in addition to the two nodes seen at Feekes 7, the tip of the flag leaf, the fourth leaf above the first node, is visible. Feekes 8 marks the beginning of the period during which we recommend that field be scouted to determine which disease is present and at what level. Septoria blotch is usually one of the first to show up. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete. Septoria reduces grain fill and the size of the grain, but usually does not affect the number of spikelets per spike, which is defined very early in the development of the plant (before Feekes 6).

Foliar fungicide applications at or before Feekes 6 are less beneficial for Septoria control than applications made at or after flag leaf emergence (Feekes 8). An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual life of the fungicide will not adequately protect the flag leaf. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas and new infections will occur, even after early applications are made. In addition, frequent rainfall may also reduce the residual effects of the early applications, making them even less effective against mid- and late-season foliar disease development.

Over the last few growing seasons, we tested several foliar fungicide programs in wheat to provide answers to question about the benefit of different application times. We evaluated the effects of single, split, and double applications of several fungicides on Septoria, powdery mildew, Stagonospora, and grain yield. Applications were made at green-up, flag leaf emergence, or at both green-up and flag leaf emergence. Applications made at flag leaf emergence did better than green-up applications in terms of foliar disease control and yield. Among the programs with double or split applications, we observed the best results with those treatments that included an application at full rate at Feekes 8-9. A single full-rate application at flag leaf emergence did just as well as or better than the green-up + flag leaf in terms of powdery mildew and Septoria control.

There are several different fungicides available for use on wheat. Refer to the Table below for a more complete list of fungicides, rates, efficacy, and pre-harvest intervals.

Source : osu.edu