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Reducing bark is biggest 2008 harvest challenge

USDA-AMS Cotton Division Classing office reports through November 13 indicate 34.3 percent of the 361,344 bales classed at Lubbock and 39.3 percent of the 118,606 bales classed at Lamesa have been marked down for bark content.

Reducing or preventing bark content in harvested cotton is one of the biggest challenges a grower faces, but is also one of the quality parameters that growers have some ability to impact with a few modifications in what they are doing in the field. History tells us that it is virtually impossible to completely eliminate barky cotton when a crop is predisposed to that unwelcome condition.

Evidence is mounting that says the combination of late, succulent cotton and an early freeze has created a huge potential for bark this year.

Fortunately, years of experience and research into the issue have provided a set of harvesting guidelines and recommendations for growers that can help reduce the appearance of bark in their harvested cotton.

The first source for guidance on this topic is the 2008 Harvest-Aid Guide published by the Texas AgriLife Extension Service.

High Plains AgriLife Extension Cotton Specialist Dr. Randy Boman notes that page eight of the 2008 Harvest-Aid Guide, (, contains a nice overview of recommendations to growers for setting up stripper harvesters to minimize the potential for bark contamination.

Two other publications can also be downloaded that provide a similar set of recommendations for reducing bark content in harvested cotton. The first is a pamphlet put out in the early 1990's by the High Plains Barky Cotton Task Force. The second is the Texas Agricultural Extension Service publication "Reducing Barky Cotton," which is of slightly newer vintage, but still contains pertinent information and strategies that can help growers combat barky cotton this harvest season.

Both publications, as well as the 2008 Harvest-aid Guide, are available for download from the Plains Cotton Growers website. Just go to the PCG Home page ( and click on the links provided.

Among the recommendations in the three publications are:

o Try to harvest cotton in the 8-10 percent moisture range.

o Make stripper adjustments and reconfigure as necessary when moving from field to field.

o Consider modification of stripper paddle rolls to reduce plant material in seed cotton.

o Don't build cotton modules on top of old cotton stalks or other crop material to avoid contamination.

o Keep field cleaners operating at manufacturer recommended speeds to prevent overloading.

Through the years, USDA-Agricultural Research Service researchers at Lubbock have determined that use of a 5 brush/1 bat or 3 brush/2 brush-bats/1 bat stripper roll configuration will generally reduce foreign matter content (particularly sticks) in seedcotton, compared to more common 3 brush/3 bat configurations.

The 2008 Harvest-aid Guide notes that it is best to time stripper rolls brush-to-bat with such patterns. The following graphic (Figure 3), copied from the 2008 Harvest-aid Guide, illustrates this configuration and timing.

Another consideration, according to Dr. John Wanjura from the USDA-ARS Cotton Production and Processing Unit, is to widen the spacing between the stripper rolls as far apart as acceptable seedcotton loss permits. An example of this is shown in the following graphic (Figure 4), also from the 2008 Harvest-aid Guide.

The wider spacing can considerably reduce stick content of stripped cotton, thus reducing potential for bark problems.

Typically plants become increasingly brittle the longer they remain in the field. In that situation growers are usually advised to consider shortening the length of paddles by 0.75 to 1 inch on brush-roll headers. This change can reduce stick content as much as 40 percent.

If shortened paddles are used, stripper rolls should be timed brush-to-brush and combing pans (mounted on the underside of the stripper heads and directly under the stripper rolls) should be adjusted to their widest spacing depending upon stripper roll spacing. A wider pan spacing at the front of the header than at the back or upper end of the stripper rolls is advisable as the largest mass of the cotton plants will be near the bottom of the stripper roll. These pans cannot be completely removed, as seedcotton losses will be excessive.

Whenever strippers are adjusted for field specific conditions to reduce bark contamination, growers should remember that some tagging (lint loss) may be acceptable, especially if the amount of foreign material can be reduced by less aggressive stripping.

The goal is to reduce the introduction of foreign material into the seedcotton and to ultimately reduce both the amount and severity of both bark and leaf trash contamination.

"There is certainly not anything out there that we would consider a magic bullet to prevent bark in cotton," concluded Boman. "With a little extra planning growers can positively impact the final quality of the cotton they produce. Weather has set this crop up to be predisposed to bark contamination, it will take a real effort from growers to minimize the adverse impact bark can have on their bottom line."

TAGS: Cotton
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