Thomas Isakeit, Professor and Extension Plant Pathologist.

Topguard (flutriafol) finally has a section 3 (full registration) label for control of Phymatotrichopsis root rot of cotton (“cotton root rot”).  This label is permanent and will permit Topguard use in all states where cotton root rot is a problem, not just Texas.  Additionally, there is also a section 18 label for Texas for 2015, which was requested just in case full registration was not granted in time for the growing season.

However, the intention of the makers of Topguard, Cheminova (under review to be merged with FMC) was that the full registration would be used with a different formulation of Topguard, known as “Topguard Terra”.  This formulation is approximately 4 times as concentrated with the active ingredient, flutriafol, as Topguard that was sold with the section 18 label.  There are no appreciable differences in the performance of the active ingredient and the properties of carriers between the formulations.  Since both formulations will be sold for the time being, it is very important that whatever formulation the grower buys, the grower pays attention to use rates printed on that container.  Eventually, probably by next year, only Topguard Terra will be available for cotton.

The Topguard that has been used for the past few years has 1.07 pounds active ingredient per gallon and is used at a rate of 16-32 fluid ounces per acre.  Topguard Terra has 4.17 pounds active ingredient per gallon and is used at a rate of 4-8 fluid ounces per acre.  Containers of these formulations will be clearly labeled (see figure 1).  Although instructions on both labels are similar, the major and obvious difference is product use rate per 1000 row feet, based on row spacing.  For example, with a 16 fluid ounce per acre rate of Topguard and a row spacing of 40 inches, 1.22 fluid ounces is applied per 1000 feet of row.   To apply that same amount of active ingredient of flutriafol in that same 40 inch row spacing, Topguard Terra would be applied at 4 fluid ounces per acre, or 0.31 fluid ounces per 1000 feet of  row.

There are no differences in the use patterns between the two Topguard formulations.  Both are still labeled for at-plant applications only, either by a T-band or modified in-furrow technique.  The modified in-furrow technique may perform better under conditions of low rainfall than the T-band technique.  The T-band technique may be preferable with fields that are sprinkler irrigated.  Ideally, irrigation or rain occurs shortly after crop emergence (several days to two weeks), to redistribute the fungicide.  The crop should never be planted dry, then watered in, because of an enhanced risk of phytotoxicity.  Unfortunately, phytotoxicity as delayed or reduced emergence may occur if there is rain before crop emergence.  Research is on-going to determine strategies to prevent such phytotoxicity, including other methods of application.

We have observed performance problems caused by clogging of application orifices.  This problem can inadvertently show that the fungicide is working (see figure 2).  Growers should pay attention to this problem, particularly first-time users.  Flow meters could identify when clogging occurs.  Different application products may alleviate the problem (e.g. larger orifices in the rebounder, or a T-band spray nozzle set higher).  First-time users should also consider leaving a small, non-treated area in the field to identify performance and allow comparisons of crop emergence.

If you have any questions, contact me at (979) 862-1340 or t-isakeit@tamu.edu.