Adapted by Nicholas Clark – UCCE Kings, Tulare & Fresno Counties & Jennifer Heguy – UCCE Merced, Stanislaus & San Joaquin Counties

While wet winters have caused sorghum acreage to decrease in recent years, early projections of water deliveries indicate that sorghum planting may once again be a necessity for some in 2018. We all know that sorghum is not corn, but successfully harvesting a quality sorghum crop became more complicated in 2016, with the appearance of sugarcane aphid (SCA).  Below are some management practice tips that may contribute to a higher quality feedstuff this fall.

Variety Selection. Work with your seed representative and nutritionist to select a variety best suited for your milk production needs. Consider yield potential and feed quality, as well as which animals will be consuming the forage. Brown midrib (BMR) trait varieties tend to be lower yielding and may be more susceptible to sugarcane aphid (SCA), but can have a higher relative feed quality (RFQ). See the 2017 Sorghum Forage Report for California Dairy for more information on variety performance. For weed management programs that include a pre- emergent herbicide, select seed that has been safened. Also consider a neonicotinoid-treated seed in order to have early protection from SCA for up to 40 days.

Stand Establishment. For optimum stand establishment, plant when there is adequate soil moisture and soil temperatures are 60 F. Target a plant population of 100,000 plants/acre (usually about 10 lbs. seed/acre, but seed weights vary). Don’t allow water stress during plant establishment, as this phase is critical for forming deep roots that make the plant more drought resilient. Control weeds which compete for water, and host diseases and pests, e.g. SCA in Johnson grass.

Fertility & water relations. Nitrogen requirements for forage sorghum are 7.9 lbs N/ ton at 30% dry matter. A 20-ton crop on N deficient soil will require an application of about 150 lbs. N. A high yielding, adequately irrigated forage sorghum will evapotranspire about 20” of water. The crop will utilize more stored soil water when water is withheld before or after flowering, but there is significant yield loss  when moisture stress is experienced before the crop flowers probably because there is less deep root development – inability to utilize  deeper soil water. If water is short, try to deficit irrigate after flowering.

Sorghum is tolerant of soil salinity up to 6.8 dS/ m before there is a yield loss. Corn, for comparison, will tolerate 1.8 dS/m before yield loss. However, beware of potential delays in  crop maturity under salinity and drought stress which can increase the opportunity time of SCA to infest the field – i.e. more insecticide treatments would be needed to protect yield.

Sugarcane Aphid Management. Why?  In 2016, when comparing the nutrient composition of SCA infested samples with non-infested samples, SCA caused significant decreases in starch and non-fibrous carbohydrates (NFC), with higher crude protein, acid detergent fiber (ADF) and ash content. Talk with your seed provider or pest control advisor (PCA) to obtain neonicotinoid-treated seed. Clothianidin and imidacloprid treated seed have been shown to offer protection from SCA for up to 40  days after planting, delaying the need for foliar applications of insecticide. During the season, scout for SCA starting in July or in the early vegetative stages, whichever is first,  weekly until the aphid is found, then semi-weekly until the threshold is reached. The PCA or scout should look at four corners of the field away from edges or irrigation borders and pick the bottom green leaf and top expanded leaf of 15 plants in each corner. Average the number of aphids per leaf. When 25% of plants have 50 aphids/leaf (a cluster about the size of a pinky fingernail), pull the trigger to spray.

Flupyradifurone (Sivanto Prime) is the only product registered in CA that is shown to consistently knock down and have good residual control of SCA in sorghum in research  across the US. Trials are currently underway in CA to explore the efficacy of other registered and experimental materials. Foliar coverage of the insecticide is as important as the timing of the application once the insect population threshold is reached. Thus, ground applications are preferable whenever field conditions allow. If an aerial application is required, use as much water as is affordable. Based on the experiences of growers in the SJV since 2016, it would be wise to include the cost of at least two over the top treatments into your production budget to evaluate potential costs for the 2018 crop year.

Harvest. Prior to harvest, communicate your goals with your silage team (nutritionist, harvester, etc.). The animals consuming the sorghum silage may dictate optimal chop length, stage of maturity at harvest, etc. Generally, it is recommended to harvest when the grains ripen  to the milk to soft dough stage. This is typically the optimal timing for quality and yield as the plant is virtually done adding biomass and the grains might be chewable by the cow or destructible by the chopper, making the nutrients more available to the animal. Deciding by grain color or days after planting can be deceiving since not all varieties have reddening grain, and environmental or management factors can delay maturity. If moisture content % is too high at  this optimal harvest stage, consider windrowing to wilt the crop before chopping and ensiling.

Take-home thoughts. Advantages of sorghum for silage include decreased seed costs, decreased fertilizer needs, and potential for  water savings. But sorghum is not corn; the quality of samples in 2016 showed lower levels of starch and NFC, with higher fiber  content than typical corn silages. Talk with your nutritionist to best determine how to incorporate sorghum into your feeding system. To simplify information, trade names of products have been used. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned.

Link to PDF Version: Considerations for a Successful Sorghum Silage Crop