Home Stretch: Evaluating Your Small Grain Crops

As we enter early to mid-June, now is a great time to assess your small grain crops to determine the overall quality. These assessments can help you determine the order of harvest, suitability of your grain for a particular market, and the potential need to contact your insurance adjuster or segregate grain. While we lack clairvoyance, there are some clues we can gather along the road to harvest to help us know what to expect once the combine starts rolling.

Evaluating Disease Pressure and Damage

Understanding the impact of late-season leaf and head diseases can allow you to anticipate your crop’s ultimate quality.  We provide a detailed look at how to scout for these diseases in a previous article you may find helpful.

Annually, we see several diseases in wheat and barley that warrant closer inspection. Some of the common diseases we can see include leaf rust in wheat and barley (Figure 1), net blotch (Figure 2) and spot blotch on barley, and Septoria tritici blotch on wheat. Powdery mildew can often also be seen in both crops, but it is important to determine if symptoms are localized in the lower canopy only or have advanced into areas around the flag leaf (Figure 3).

Assessing Fusarium head scab (FHB) is also important at this time of year. We recommended examining a minimum of 100 heads by sampling in ten sections of the field, 10 heads per section. Symptoms can commonly be found on individual kernels to the whole head depending on the variety, fungicide application and timing, and risk of FHB when infection occurs. We recommend starting to scout for FHB approximately three weeks following flowering, as this can also help determine if mycotoxin contamination is possible.

Estimating Yield

It is impossible to get a perfect forecast of yield ahead of harvest, but there are ways to obtain a relative understanding of the potential for your fields.

The more samples obtained from a field, the more accurate the yield assessment. We recommend sampling a minimum of 3 random locations per field. Avoid sampling in or around bordering rows and areas adjacent to wheel tracks, field edges, errant weedy patches, particularly wet or dry spots, or sprayer overlap zones (often found in field corners). Do the following steps at each sample location in the field:

1. Count the number of heads in 5 feet of row. Count only what will be harvested by the combine, and viable heads. For instance, very late tillers often have heads that are too short or do not have many viable seeds, so they should not be counted.
2. Divide step 1 by 5 to get the number of heads per foot of row.
3. Out of the 5 feet of sampled row, randomly choose at least 3 heads, and count the number of spikelets per head. This value often ranges from 6 to 12. Only count spikelets that have 2 or more kernels (Figure 1a-b)
4. On each of those randomly chosen heads, estimate the number of kernels per spikelet. This value often ranges from 2-3. (Figure 1c-d)
5. Heads per foot × spikelets per head × kernels per spikelet ÷ row spacing × 0.48 = bushels per acre

Lastly, add up all your yield estimates and divide by the number of sites sampled to find the average yield estimate in bushels per acre for the whole field. Remember that these estimates are just that, and they may not match what you see on the yield monitor. Diseases can rob yield by reducing the weight of kernels or the total number of viable kernels in the field; weather also plays a role in grain fill and can cause other pre-harvest loss issues, like lodging. Harvest losses due to timing of harvest and combine settings are also a possibility.

While this approach can provide a snapshot of the potential in any one area of any one field, remember that more information is better, and practicing this technique in several spots will improve accuracy.  Also, consider other factors that may constrain yield across your fields, including lodging, variation in soil properties, and uneven heading.