Wheat growth stage and foliar fungicide applications
Cool conditions over the last few weeks have slowed the wheat down considerably in Ohio, however, the development of the crop is still about a week or two ahead of what is considered to be normal in Ohio at this time of year. Current growth stages range from Feekes 6, jointing, to Feekes 8, flag leaf emergence. However, the different between these growth stages cannot be determined just by looking at the height of the crop from the road, since relatively low temperatures and dry conditions may have prevented some varieties from reaching the height that is expected when the crop is between at Feekes GS 6 and 8.
Figure 2. Side-by-side wheat plants of different height all at Feekes 8; note that the two nodes are visible above the soil line, plus the flag leaf is just beginning to emerge on all three plants. Remember, short-looking wheat does not mean that the crop is not developing and advancing through the different growth stages. Growers who rely on the height of the crop as an indicator of crop development may miss Feekes GS 6, a critical growth stage for herbicide application, and Feekes 8, a critical stage for managing foliar diseases with fungicides. Do not relay on the height of the plants or calendar dates alone to make your management decisions. Walk fields, pull tillers from multiple places, remove the lower leaves, and examine these tillers for the presence of nodes and the emergence of the flag leaf. 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 (Figure 1). As shown in Figure 2, plants of different heights and sizes may all be at the same growth stage (Feekes 8 in this case).
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, and it already has been reported in some fields. 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. Like many other foliar diseases such as Stagonospora, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an important yield component that is defined very early in the development of the plant (before Feekes 6). As a result, a foliar fungicide application at green-up or jointing is less likely to be as beneficial for Septoria and Stagonospiora control as an application made at or after flag leaf emergence.
An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual effects 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 have been made. In addition, frequent rainfall may also reduce the residual effects of the early fungicide applications, making them even less effective against mid- and late-season foliar disease development. Results from previous studies have shown that the greatest benefits from foliar fungicide applications were obtained when applications were made between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9.
There are several different fungicides available for use on wheat. If powdery mildew is the target disease then Tilt or PropiMax should be applied. Tilt, PropiMax, Quadris, Quilt, Stratego, and Headline have good efficacy against Stagonospora leaf blotch, other leaf blotch diseases and leaf rust. Obtain current pricing of fungicides to determine the most economical control option. Use 20 gallons of water per acre with ground equipment and 5 gal water/A if applying by airplane. Using less water will lower effectiveness. Check labels for application timing restrictions.