Hutmacher reminds growers and PCAs that the time from the seedling stage (couple of true leaves) through about first bloom stage is considered the easiest time of the year to find and identify this problem while it is still a relatively early infestation.

Identifying it early will allow the grower to initiate containment practices that can slow down the spread of the pathogen. This could include such things as cleaning as much soil as possible from equipment before moving from an infected area to a clean area.

If the disease is identified through a lab sample, make a permanent note of the locations on field maps, limit to the degree workable practices that move soil and plant debris out of infested fields into clean fields, and plant resistant varieties, suggests Hutmacher.

Race 4 fusarium symptoms can begin very early on, starting when plants only have one or two true leaves. Foliar symptoms include patchy leaf yellowing and necrosis that typically begin on the leaf margins of lower leaves, but these symptoms are not always easy to differentiate from those with other seedling diseases.

The most useful diagnostic characteristics that suggest possible FOV are: (1) the wilting of leaves and stems seen even under mild early season weather conditions; combined with (2) the dark brown stains seen in the vascular core of the tap root when you pull or dig up a plant, slice the root lengthwise and examine it. Growers should note that FOV damage is most easily seen as an early season disease with most damage visible in the seedling stage. This contrast with  the late-season (boll maturation) period more when verticillium wilt typically develops and causes the most damage.

Hutmacher said vascular staining caused by FOV also typically looks different than vascular staining seen in verticillium wilt. Race 4 FOV staining is more of a continuous, dark brown color most easily observed in the tap root, while vascular staining seen with verticillium is a more irregular, flecking stain of the vascular system.

More detailed guidelines for fusarium sampling and recommendations for containment practices are on the UC Cotton website: http://cottoninfo.ucdavis.edu.

hcline@farmpress.com