Wheat and barley crops are susceptible to lodging, the bending over of the stems near the ground level. The incidence of lodging has been greatly reduced by the introduction of short, stiff-straw cultivars of the Green Revolution in the 1960s and 1970s.
Lodging is still a problem particularly with high inputs of nitrogen fertilizer and water. Lodging is undesirable due to uneven maturity of the crop, increased moisture content of the grain, decreased grain quality due to grain shriveling as measured by test weight, and increased harvesting costs.
Plant growth regulators help control lodging in wheat and barley. Herbicides, fungicides, and various cultural practices and environmental conditions can also impact lodging.
Various compounds have been used as plant growth regulators in small grains worldwide. Ethephon (Cerone), chlormequat chloride (Cycocel), mepiquat chloride, and trinexapac-ethyl have been used on wheat and barley to control lodging especially in Europe.
In the U.S., ethephon, marketed as Cerone in wheat and barley, is the only plant growth regulator registered for wheat and barley. Ethephon is marketed as Prep for use in cotton as a growth regulator. Chlormequat chloride and trinexapac-ethyl are only registered for turf and ornamentals in the U.S. and are used to suppress growth. Mepiquat chloride is registered for U.S. use in cotton only as a growth regulator and harvest aid.
The use of plant growth regulators on small grains is uncommon in Arizona. Cerone has been used on wheat and barley in the state, primarily in the Willcox area on up to a third of the small grain crop depending on the year.
Lodging is a problem in the Yuma area, but Cerone is generally not applied since the temperature needs to range from 35 and 90 degrees F. for five days after the application. High temperature often exceeds this range during the appropriate time for application.
Cerone is the only plant growth regulator registered for lodging control in wheat and barley in the U.S. Cerone decomposes in the plant to release ethylene, a naturally-occurring plant growth regulator. Cerone reduces lodging by decreasing plant height by one to six inches and increasing the strength of the straw.
The last two to three internodes are shortened by this chemical, particularly the top internode referred to as the peduncle. Cerone also reduces the tendency of barley heads to “neck” towards the ground and for heads to fall off the plant.
The timing of application of Cerone is important for the chemical to be effective and not cause crop injury. Cerone should be applied from the emergence of the last leaf (flag leaf) to the late boot stage, but before the awns emerge. This window of application will last from five to 14 days depending on the weather.
The heads should never be exposed to spray solutions as might occur in cases where the head splits the boot open or the head has emerged. Rain or overhead irrigation received less than six hours after application will reduce or eliminate the chemical’s efficacy.
The rate to apply Cerone depends on the expected severity of lodging and whether the crop is wheat or barley. Cerone should not be applied in irrigation water, tank-mixed with herbicides or nitrogen solutions, or mixed with adjuvants, surfactants, and wetting agents.
Cerone should be applied to vigorously growing crops likely to experience significant yield loss due to lodging. In the absence of lodging, Cerone can reduce yields. Cerone should not be applied to a crop stressed by water, insects, or disease.
The plant growth regulator released by Cerone, ethylene, increases the resistance of water flow through the leaf. Therefore, crop injury can occur if the temperatures are above 90 degrees F or under windy conditions where crop water demand is increased.
Cerone requires seven days to become activated in the plant and is not effective in reducing lodging during or before this time period. Cerone delays heading by one to two days and maturity by one to four days, but not any longer than the delay in maturity that might occur if the crop is lodged.
Herbicides can affect lodging in small grains especially if applied outside the recommended crop growth stages. The herbicide 2,4D applied later than the boot stage may increase lodging particularly in barley.
Lipid synthesis inhibitors including Puma applied after the first node appears can weaken the stem and make the crop more susceptible to lodging. An example of herbicide-reduced lodging is MCPA applied at the two-leaf stage to wheat, which may also reduce yield. It is not recommended to apply herbicides contrary to labeled rates and timing with the intent of causing slight crop injury leading to reduced tillering, height, and lodging.
A group of fungicides known as strobilurins, including Headline, have shown to reduce lodging in small grains in production areas outside of Arizona where diseases are a problem.
These fungicides may reduce lodging by inhibiting growth of fungal organisms in the lower stem. The lower stem in small grains tends to be solid rather than hollow, and this contributes to straw strength. The stem in small grains becomes progressively more hollow as the plant matures, and the extent of this characteristic varies with cultivar and growing conditions.
The application of fungicides to wheat and barley in Arizona is generally not economical or effective except in certain cases. It is not recommended to apply of any fungicides, even strobilurins, in Arizona with the intent of reducing lodging.
The susceptibility of a small grain crop to lodging is greatly influenced by crop species, cultivar, and cultural practices. Barley is generally more susceptible to lodging than wheat because barley stems are weaker since barley has fewer straw-strengthening compounds including lignin. Taller cultivars are generally more susceptible to lodging than shorter ones.
Early planting, narrow-row spacing, high seeding rates, excessive nitrogen rates, and excessive irrigation contribute to increasing the susceptibility to lodging. Excess water and fertilizer during the stem elongation stage especially can increase the risk of lodging, but nitrogen and water deficiencies during this time period can also reduce yield potential.
Lodging often occurs near the end of the season during the last irrigation if windy conditions exist. Lodging is generally more common on heavy soils due to the relatively high water and nutrient holding capacity. If small grains are grown following vegetable crops, lodging can be a problem due to high levels of nitrogen fertilizer remaining in the soil after the vegetable crop.
If a small grain crop is slightly leaning but not lodged, then a good balance has been obtained between high yields and minimal lodging.