News > 2020.10.08 CFS Growing Insights

2020.10.08 CFS Growing Insights

Oct 08, 2020

Harvest Update
Sunday, October 4th recorded 61% of MN soybeans harvested, according to the NASS Crop Progress Report. This is up from 31% from the week prior and significantly above the 5-year average at 35%, and 7% harvested in 2019 on the same date. Corn harvest has started as well, with Oct. 4th progress across MN at 14%, up from 6% the week before. Harvest last year was at 1% and the 5-year average currently sits at 7%.
Factors Leading to Stalk Rot
Signs of stalk rots are appearing throughout fields across southern MN in 2020. Many plants tolerated cool soils at planting and several cycles of wet/dry soil conditions this year. Stressful growing conditions combined with crown decay can create a more susceptible platform for late-season stalk rots. Stresses such as wet soils, cold temperatures, soil compaction, fertility problems or herbicide injury; along with the current weather pattern, a wet spring followed by cooler temperatures, may amplify the effects of these problems. Injury to roots, stalks or leaves by diseases, insects, nematodes, hail or equipment also can increase the incidence of stalk rot by providing avenues of entry and overlaying multiple stresses. High yields are frequently associated with stalk rot problems. Plants can over-commit to yield when environments are ideal through the pollination period and stress occurs later in the season. In a stressful environment, the large number of kernels places a high demand on the plant for sugars. If photosynthesis is reduced because of stress, the kernels draw stored photosynthates from stalk tissue and deprive the roots of adequate nutrients. Once the kernels begin taking sugars from storage areas (cannibalization), it cannot be reversed. Cases where high nitrogen levels combined with low levels of potassium may increase the development rate of stalk rots. However, balancing the proper rate of nitrogen with adequate rates of potassium and phosphorus will decrease the potential for stalk rot in any yield environment.
How does Stalk Rot Develop?
Corn produces sugar by means of photosynthesis. Sugar, the energy source of all cells, moves to growing points in the stalk and roots during vegetative growth. After pollination, priority for sugar shifts to developing kernels. Approximately 80% of the sugar demand for grain fill is met by photosynthesis, while the remaining 20% comes from storage in the stalk. After pollination, some of the sugars from the stalk are used for cell maintenance throughout the plant. If stress reduces photosynthetic capabilities, more sugars are taken from the stalk to meet grain fill demand. If insufficient sugar is produced, stalks and roots will eventually be weakened, allowing stalk rot organisms to invade earlier and breakdown or plug up tissue.

Two different methods can be used to scout out stalk rots: the push test or pinch test.
  1. PUSH TEST: Randomly select 20 plants from five different areas of the corn field (100 plants total). Push the top portion of the plant, and note whether the plant lodged or had the stalk strength to remain standing.
  2. PINCH OR SQUEEZE TEST: an assessment of the lower stalk. Again, randomly select 20 plants from five different areas of the corn field (100 plants total). Remove the lower leaves and pinch or squeeze the stalk above the brace roots. If the stalk is easily squeezed, with moderate pressure, it is rotting on the inside. Record the number of rotted stalks.
Regardless of which method is used, if 10 to 15 percent of the plants are lodged, stalk rot is prevalent in the field. If this condition occurs, early harvesting should be considered to prevent losses as the corn stalks will have less time to rot, and subsequently lodge in the field. Extra grain drying costs may be incurred, although those costs could be covered by better harvest efficiency.

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