Though little to no wheat is planted this season, we are still looking at other small grains and forages for winter weeds. Yesterday, we were looking at wild radish in oats that need to be treated. Sometimes we have injury reported after using broadleaf herbicides in small grain, particularly oats. There are many things that influence herbicide injury, but the timing of our broadleaf products, such as 2,4-D and MCPA is critical in small grains.
UGA Extension Weed Scientist Dr. Stanley Culpepper says we do not need to use 2,4-D and MCPA until we have full tiller and before jointing.
What is full tiller? Following emergence and the spike stage, small grain crops begin to tiller. These are essentially stems that will produce a grain head in the future. When we have 4, 5, or 6 tillers on a plant, it is considered full tiller. Depending on growing degree days, it will generally take between 20 and 35 days to reach full tiller.
We looked at two oat fields yesterday – one planted in October and one in November. The later planted field had just 3 tillers per plant (above) where the older field had 5 tillers. The difference here and in other small grain is that these oats are planted for grazing only. Therefore, we have less concern over injury. It will be fine to go ahead and treat both fields.
With the same herbicides, we don’t want to treat once crop enters the jointing stage. Just before jointing, the stems will elongate. At the base of the stem, you will feel a swelling of the stem (almost like a bee bee inside the stem) which is the first node or joint. The joint is the growing point. The plants have now moved into the reproductive growth stages. Here is a shot of growth development from the 2015-2016 UGA Wheat Production Guide.