Harvest Considerations for Drought Impacted Crops
The 2018 growing season has been tough to say the least. Early season heat, very low soil moisture, and severe lack of rainfall during the growing season has drastically impacted crop health, plant uniformity, and overall yield. The impact of these conditions extends beyond the growing season to harvest and grain storage. Here are some factors to consider:
Drought conditions leads to crop stress and may contribute to development of various stalk diseases. It is imperative to check fields leading up to harvest for stalk integrity and prioritize fields with the most stalk damage and weakest stalks. Weak stalks can lead to issues such as lodging and ultimately lost grain.
There are several diseases we may be seeing infect stalks, such as charcoal stem rot, fusarium stalk rot, and anthracnose stalk rot. Charcoal stem rot is evident on the inside of the stalks as a gray to black discoloration from the fungal structures. This disease is more common in drought years. Fusarium stalk rot is identified by either a white growth at the nodes on the outside of the plant, or as a pink color in the very center of the stalk. Finally, Anthracnose shows up as black patches on the outside of the stalk. These diseases cause a deterioration of the crop and can be tested with either the pinch or push tests.
Charcoal rot, anthracnose, fusarium stalk rot. (Photo courtesy of the University of Nebraska CropWatch)
The pinch and push tests help identify crops that are at risk from stalk diseases. According to the University of Nebraska, a sample of 100 plants should be selected representing a large portion of the field. Grab the top end of the plant and push the stalk away from you to about 30 degrees. Let go of the plant to see how the plant reacts. If the plant does not return to vertical, the plant likely has stalk rot issues that need to be accounted for.
The pinch test is conducted at the lower internodes of the plant. Pinch a plant between the lower nodes to test how easy the stem can be crushed. If the stalk crushes easily, the plant likely has some damage due to stalk rots. Fields with more than 10% of the plants with stalks with reduced integrity should be prioritized for harvesting.
Conduct pinch and push tests on all fields to find fields most affected by stalk rots. Prioritize these fields for harvest first to minimize losses from lodging and grain loss.
Foliar and Grain Diseases
You may recall in other dry growing seasons, large clouds of black, sooty, dust during harvest. These are often caused by a fungus called Alternaria but can be attributed to many other fungal diseases. We can also see late season growth of southern rust that can turn black and be shed off plant leaf surfaces. Generally, these diseases are not an issue for human health, however should be avoided by individuals with respiratory issues. Overall, these diseases won’t affect yield quality, but will deteriorate leaf tissue while still on the stalk.
The hot and dry conditions can also lead to aspergillus ear rot. This can be identified by olive-green spores on damaged kernels. This fungal disease is capable of producing aflatoxin but will not necessarily do so. However, production of aflatoxin is variable, but more common if the crop is drought stressed. If aflatoxin is produced, levels can accumulate to dangerous levels that would be toxic for human or animal consumption. If that is the case, grain would be docked or rejected at the elevator. Overall, the chemical group aflatoxin belongs to, mycotoxins, are relatively common and not dangerous at low levels. It is important to note that the presence of aspergillus ear rot does not necessarily indicate that the crop has aflatoxin. Grain elevators will often use a blacklight to identify aflatoxin. However, the blacklight simply detects kojic acid. Kojic acid and aflatoxin are both produced by the same fungus, however presence of kojic acid doesn’t necessarily indicate the presence of aflatoxin. This method can often lead to false positives and result in rejection or dockage of grain needlessly.
Fields subjected to more moisture and heat stress as well as fields that had higher levels of ear feeding likely from corn ear worms are more at risk for aflatoxin.
Combine Settings for Drought Impacted Crops
Adjustments to combine settings will need to be made to adjust for smaller ear size and weaker stalks. Slower travel speeds will be necessarily to help feed stalks into the combine. Cobs may be rubbery and difficult to thresh. The University of Nebraska recommends “On the cornhead, the gap between snapping plates above the stalk rolls should be adjusted so that the ear butt is held on the plates above the rolls but with enough room for stalks to be pulled through without wedging. A gap of 1.25 inches used in normal years will likely need to be narrowed closer to just over an inch to avoid butt shelling of smaller diameter ears.” Because we have less material to pull through the combine, concave clearance should be narrowed. Additionally, keep rotor or cylinder speeds slower than normal without cracking seed coats. The sieve openings in the cleaning shoe may need to be adjusted smaller to account for small kernel sizes. If adjusted too small, grain can be sent back through in the tailing return, so attempt to fine tune this adjustment.
In soybeans, if seeds are lighter than normal, normal fan speeds may blow seeds out the back. Adjust fan speeds to accommodate. Drought stressed beans may also be difficult to clean and brittle.
Grain Quality and Storage
Seeds that are damaged during harvest are more likely to develop fungal diseases which can cause problems during storage. If a large portion of the seeds are damaged, broken kernels and fines should be removed before storage. Leveling of bins will be of particular importance to maintain even airflow through the grain. Even so, grain should be monitored for hotspots caused by fungal diseases and moisture. If you think you may have molds that can produce mycotoxins, it is recommended that grain be dried down to 14%. If grain is going to be stored long term, dry grain to 13%. Additionally, as you are filling the bin with grain that may have mycotoxins, only fill to a quarter full initially until grain is dried and cooled down. Repeat this process as you are filling the bin. To best maintain grain quality in the bin, cool the grain whenever possible. If the temperature outside the bin is 10 degrees below the grain temperature, you should run the fans. Repeat this until the grain temperature reaches 30 degrees. This should help maintain grain quality as long as possible. However, it would still be advised to sell or market grain as early as possible.
Cleaning of bins and equipment will be necessary if dealing with molds, fungus, and mycotoxins. Clean up the combine grain tank, heads and other surfaces with a solution of ¾ cup of bleach for each gallon of water. Maintain good ventilation when cleaning. This should be completed inside grain bins after moldy crop has been removed. This disinfecting solution can be sprayed on the bin surfaces to clean up any remaining mold.
As plant tissue continues to dry down, the risk of fire will increase. Here are some precautions to take moving into harvest. Listen for worn bearings or rubbing parts that may produce a spark. Visually inspect belts that may be worn. The same goes for exposed wires and damaged insulation. Clean off residue and chaff from around moving parts regularly and across the whole combine to minimize combustible material. If you smell smoke, stop and inspect the combine immediately. Residue may smolder for some time before igniting giving you time to prevent a fire. It is best to start on the downwind side of a field. This would save standing crop on the chance a fire did start.
Come prepared to the field. It might be wise to bring some tillage equipment or a water tank to the field. Always keep fire extinguishers on each piece of equipment.