The development of resistance by microorganisms to various plant health products is a present and on-going problem. History has shown that when an organism develops resistance to one compound, that resistance is expressed toward all other compounds within the same "class of chemistry." Research has also shown that within many microorganism populations individuals already exist that express a tendency toward resistance or are resistant to a given class of chemistry at the time a new chemical is introduced.
In order to help manage and retard the development of resistance, it is necessary to use different classes of chemistry, so that the microorganism population has a more difficult time establishing a resistant population. Theoretically, a microorganism population, exposed to a number of chemical classes with various modes of action, will be less likely to develop a population with resistance to any one of these chemistries.
Establishing to which chemical class a plant health product belongs, can be a problem. Trade names are little to no help. Even looking at the active ingredient on the container often is little help, unless you are a chemist. The following list of chemical classes and associated trade names was recently published in the Tree Fruit magazine. It is presented here to help you sort out various fungicides and help you improve your resistance management program for disease control.
| Trade Name | |
| Dicarboximide | Rovral (iprodione) |
| Hydroxyanilide | Elevate (fenhexamid) |
| Imidazole | Procure (triflumizole) |
| Phenylpyrrole | Medallion/Scholar (fludioxinio) |
| Piperazine | Funginex (triforine) |
| Pyrimidinmine | Vangard (cyprodonil) |
| Pyrimidine | Rubigan (Fenarimol) |
| Strobilurins | Flint (trifloxystrobin) |
| Abound (azoxystrobin) | |
| Triazole | Break/Orbit |
| (sterol inhibitors) | (propicanazole) |
| Elite (tebuconazole) | |
| Rally (myclobutanil) |
Avocado Thrips Update
Recent research developments, concerning the management and control of avocado thrips, were recently published in the Citrograph magazine. If you would like a copy of this article, please contact me - 805/934-6240.
Leafminers in Basil
Novartis Crop Protection has recently been granted a section 18 for all California counties for the use of AgriMek for leafminer control in basil. Suggested rates are: 8-16 oz. per acre, at 7-day intervals in a minimum of 50 gal. of water. Do not apply more than 48 oz. per acre per cropping season. Apply by ground only. The REI is 12 hours, and the PHI is 14 days. Call your Novartis representative if you have questions. This section 18 expires September 30, 1999.
Infected leaves of stocks exhibit chlorotic areas on their top surface and slight twisting. The underside of leaves shows extensive white fungal growth. Infected leaves turn yellow, then brown, and prematurely fall.
Several varieties of Brassicas are infected by this fungus, but spores from other Brassicas (i.e., broccoli) will not infect stocks. Matthiola incana and M. bicornis are both susceptible. None of the cultivated stocks show resistance to this fungus, but differences in sporulation have been reported between cultivars.
This disease has become epidemic in the Lompoc Valley in just a few months despite multiple fungicide applications.
Successful IPM programs that reduce downy mildew losses in other pathosystems include seed treatments, controlled watering, improved ventilation, balanced nutrition, strict sanitation, and combinations of contact and systemic fungicides applied on a calendar schedule.
Peronospora parasitica has been reported infecting stocks in Ventura and Santa Barbara Counties. It has previously been reported as a serious problem in Australia.
1Heather Scheck, Plant Pathologist, Santa Barbara County Agricultural Commissioner's office.
