By Edwin Lentz, Pierce Paul, Mark Loux, Ohio State University
The above average temperatures over the past few weeks may have accelerated the development of the wheat crop. It is important to know when the crop has matured to Feekes Growth Stage 6 (initial stem elongation or jointing). Basically the crop switches from vegetative growth to reproductive at this time and can be visually determined when the first node is observed above the soil surface. To check for this node, dig up plants from multiple locations in the field, remove the secondary (smaller) tillers and observe the main stem (may appear as large tillers). Gently pull down the lowest two leaves (including the sheath around the stem) one at a time to the base of the tiller. If there is a swollen area, or an area that is slightly a different shade of green than the rest of the stem, then the first node is present. It is generally located about an inch above the soil surface. At early Growth Stage 6, the node is only detected by pulling down the lower leaves, as the plant matures, the node (a bump) can be detected by running the fingers along the base of the stem. If two nodes are present, the field is at the next growth stage, Feekes 7.
Growth Stage 6 is an important developmental time for the crop which should be reflected in management practices. Top dressing of N needs to be completed by or soon after this stage since the crop will rapidly uptake N from this point until flowering. OSU research has shown a 10 percent to 15 percent yield reduction when the first spring application of N did not occur until late stem elongation (Feekes Growth Stage 9). Also, labels for several wheat herbicides indicate that the product should no longer be applied after jointing due to the risk of yield loss. Dicamba is the primary herbicide of concern here, but the labels for some 2,4-D products also state that application should occur prior to jointing. OSU research has generally shown that 2,4-D can be applied past jointing and prior to joint with minimal risk of injury, but it’s important to use a 2,4-D product that supports this use.
In recent years, some producers have applied or shown an interest in applying foliar fungicides at Growth Stage 6 without disease pressure. This questionable practice generally makes a half-rate application at Feekes 5-6 followed by a second half-rate or full rate at or after Feekes 8 (flag leaf emergence). OSU research to date has shown that yield response to these early applications of fungicides is highly variable and depends on how early and how much disease develops. For instance the results from six fungicide trials showed yield responses ranging from -1.1 to 7 bushels/acre. This 7-bushel yield increase was observed in an inoculated trial in which final disease severity on the flag leaf was more than 90 percent in the check compared to 68 percent in the fungicide treated plot. Inoculations had been done in the fall which led to an increased early disease development in the spring. Unnecessary use of fungicides and applications at half-rates increase the risk of fungi developing resistance to these products, making them ineffective when they are really needed to manage diseases. So even if early half-rate fungicide use occasionally leads to a marginal yield increase, this practice may result in the loss of efficacy of valuable fungicides.