February 13, 2001
Strobilurin Fungicides for Squash and Tomato
Mark C. Black, Extension Plant Pathologist
Texas Agricultural Extension Service
Texas A&M University, Uvalde
Fungicides are only one part of your disease control strategy. A new fungicide class, strobilurins, is now available as azoxystrobin (Quadris) and trifloxystrobin (Flint). These active ingredients are analogs of strobilurin A, a naturally occurring compound produced by a mushroom fungus. They have a CAUTION action word and are considered to have low toxicity.
General Vegetable Disease Control Principles
1) Buy disease-free seeds or transplants from reputable sources.
2) Long rotations between any related crops (1 year effect < 2 years < 3 years) to starve out many of the pathogens in debris and soil.
Squash is related to, and has most of the same diseases as other cucurbit crops: cantaloupe/melon, cucumber, pumpkin, balsam pear, gourd, watermelon, and waxgourd. Cucurbit weeds include buffalo gourd and citron metlon.
Tomato is related to, and has most of the same diseases as other solanaceous crops: pepper, eggplant, tomatillo, and potato.
3) Within a season, separate fields of the same or related crops with as much time and space as possible.
4) Broadleaf weed control in and around fields, along fences, and in ditches. This should include volunteer vegetable plants!!
5) Use varieties with partial disease resistance, if available.
6) Use drip or furrow irrigation; if only overhead irrigation is available, apply irrigation in early morning so canopy will dry quickly.
7) Avoid working or harvesting the fields when leaves are wet from dew, rain, or irrigation.
8) Design a fungicide spray program based on:
Ž disease history in each field; what have been the most limiting factors (insect, disease, weather???)
Ž prevailing weather conditions
Ž frequent field
scouting---When does each disease start?
---What is the disease incidence/severity?
Ž cost of each fungicide product
Ž crop market price and shipping opportunities
Ž threat of crop loss from virus diseases that we cannot control.
9) Preventative treatments before a disease starts are almost always more effective than A rescue@ treatments after you detect a disease.
10) Do not use just one fungicide class (see Table 1). Continued exclusive use of a certain fungicide class may allow a fungus population to develop that is tolerant of that product (A fungicide resistance@ ).
11) Terminate a crop as soon as possible after the last harvest, usually by plowing out the roots. This will stop most pathogen buildup in debris and soil.
Table 1. Fungicide classes used in squash and tomato production and potential for A fungicide resistance@ if used exclusively and continuously.
|
Class |
Resistance Risk |
Active Ingredient |
|
| strobilurin | Yes | azoxystrobin trifloxtstrobin |
Quadris (Abound, Heritage) Flint |
| plant activator | No (?) | acibenzolar | Actigard (tomato) |
| triazole | Yes | myclobutanil | Nova |
| phosphate | Yes (?) | fosetyl-aluminum | Aliette |
| acylalanine | Yes | mefenoxam | Ridomil Gold and mixtures Apron, Ultra Flourish, Allegiance, etc. |
| benzimidazole | Yes | benomyl thiophanate methyl |
Benlate Topsin-M (Tops, Cleary's 3336, Thiphan) |
| substituted benzene |
No | chlorothalonil |
Bravo, Terranil, Agronil, Equis, mixtures PCNB, Terraclor (tomato) |
| carbamate | No | EBDC (mancozeb, maneb) | Dithane, Manzate, Maneb, Penncozeb, Ziram, etc. |
| copper | No (fungi) Yes (bacteria) |
fixed copper | Champion, Champ, Basic Cooper Sulfate, KOP-Hydroxide, Basicop, Kocide, Nu-Cop, Top Cop, etc. |
| sulfur | No | sulfur | Sulfur, Golden-Dew, Bensul, Kumulus, Thiolux, etc. |
| salt | No | potassium bicarbonate | Armicarb |
| petroleum oil | No | parraffinic oil | JMS Stylet-Oil, Sunspray |
| fatty acid | No | fatty acid (potassium salt) | M-Pede |
| biological | No (?) | beneficial fungus (Ampelomyces quisqualis) |
AQ 10
|
TAKE HOME MESSAGE: MIX a
A Yes@
product with a A No@
product
OR ALTERNATE a A Yes@
product with a A No@
product
IF the labels permit that particular tank mix.
Table 2. Relative effectiveness of various chemicals for cucurbit disease control (on the Internet at http://ipmwww.ncsu.edu/agchem/chptr6/615.pdf)
Selected squash and tomato fungicide efficacy trials, most with strobilurin fungicide treatments, from various states from Fungicide and Nematicide Tests for Control of Plant Diseases, APS, St. Paul, MN at http://www.apsnet.org