This spring has been a challenging one for many producers throughout the state. Most crops have struggled at some point during the spring. To date the Oklahoma sorghum crop this year can be fit into three categories, with some growers dealing with all three. Oklahoma sorghum producers are not immune to this and their seasons can probably be fit into three general categories. First are that growers were able to get the crop in a timely manner, had good conditions, and the crop is up and growing. While we would like to see this on most acres, this has not been the case. Most of the sorghum fell into the other two categories. Either growers have not been able to get into their fields and still have sorghum in bags waiting to be planted or were able to be planted but have marginal stands. For growers that have yet to plant, the question has become whether or not to continue with grain sorghum planting. While most growers have to work through the financials on their individual farms, growers still have the ability to establish fields and be quite productive. Historically, we have advised growers at this stage to hold off planting until late-season in order to minimize the impact of traditionally challenging environmental conditions experience in late-June and early-July. However, sugarcane aphids have made the success of late season crop more dependent on insecticide applications. Therefore, if growers are willing to budget 2 insecticide applications and be proactive on scouting and applications, this is still a potential option. Other growers that have stands in the field and question on whether to maintain stands or terminate and replant. This can be a difficult discussion and there can be quite a few things growers must consider before making this decision. As a general rule, if growers have between 18k-20k active plants per acre, adequate yields can still be achieved without an additional seeds planted, especially this late in the season and if the plants still have a reasonably even stands. If stands are spotty or skipping, growers can decide to plant certain areas of the field, while maintaining others. If growers have less than 18k active plants per acre and growers decide that replanting must occur, several times growers can get away with over-seeding the crop over the current stands as opposed to completely terminating and completely replanting. If growers over-seed, it is recommended that growers look at planting around half of the initial seeding rate.
The validity of this critical 18k plant population to maintain a crop depends on several factors. As previously mentioned stand distribution is a critical component. An even stand can maintain high enough canopy coverage to cover the soil surface in order to help maintain soil moisture and help compete against weeds. Another critical aspect is the hybrid that was planted. Hybrids that have lower tillering potential would require higher populations to achieve adequate yields. Without these tillers there just might not be enough heads/acre in order to maintain yields. However, hybrids with better tillering potential can sustain these lower populations while still maintaining adequate yields.
When growers have achieved stands, both weed control and fertility issues start to emerge. If growers have made a large application on fertilizer preplant, especially N, with the current weather patterns we have experienced in the las several weeks, a good portion of this may have already been denitrified or leached deep into the soil profile. This means growers need to be proactive with side-dress applications. To trigger these, growers best option is to make sure to have N-rich strips throughout their fields. If not, growers need to look for overly pale, stunted sorghum and be timely with an application. Nitrogen fertilizer is not the only thing influenced by the moisture in these fields. High levels of moisture and decrease the efficacy of many preplant herbicide programs. Growers many need to make subsequent herbicide applications. This becomes very critical as several chemicals need to be applied prior to the sorghum plant reaches ~30 inches tall.
Sorghum stands with uneven stands (left) of even (right), those on the right still might produce adequate yields.
The challenges that this summer will hold for sorghum producers is still in question. However, it must be noted that sugarcane aphid numbers are growing and moving north through Texas. MyField website numbers as of May 25th, indicate the shift from populations solely in the Gulf Coast to several populations moving into south-central Texas. While there is little need for Oklahoma producers to be concerned at this point, growers need to make sure they are aware of the moving population. If growers are active on their scouting management plans and timely with insecticide applications, most growers in recent years have noted minimal impact of the pest on overall yields. However, if growers get behind, sugarcane aphids will be a challenge for them throughout the season. Currently OSU recommendation for applications are an average of 100 aphids per leaf blade. To scout for aphids, growers need to identify 4 to 5 locations that are representative of the field and collect 5 to 6 plants at each location. For each plant, growers need to look at the underside of the lowest most fully green leaf and the high most fully developed leaf. If the plant is at flag leaf or later in reproductive stages, growers should scout the leaf under the flag leaf. While counting aphids in-field on leaves can be a challenge, a good rule of thumb is 100 aphids per leaf is approximately the size of a quarter to half dollar. As populations tend to congregate on the leaves, growers should also look for multiple smaller populations.