Effect of Selected Pesticides on Survival ofColletotrichum gloeosporioidesf. sp.malvae, a Bioherbicide for Round-leaved Mallow (Malva pusilla)

Abstract

Commercial formulations of 33 herbicides, 12 fungicides, and 16 adjuvants were evaluated for their toxic effects on germination ofColletotrichum gloeosporioidesf. sp.malvae(C.g.m.) spores. At the recommended rates, none of the herbicides for grass weed control (diclofop, difenzoquat, fenoxaprop-ethyl, flamprop-methyl, and sethoxydim) or formulated herbicides registered for both broadleaf and grass weed control [diclofop plus bromoxynil (23:8), propanil, and propanil plus MCPA (7:2)] were compatible with C.g.m. spores. C.g.m. spore germination and appressorial formation recorded 24 h after exposure were totally inhibited by these herbicides. At recommended rates, herbicides for broadleaf weed control (2,4-D ester, 2,4-D amine, benazolin, bentazon, clopyralid, cyanazine, cyanazine plus MCPA (1:2), dicamba, dicamba plus MCPA (1:4), dicamba plus mecoprop plus MCPA (1:1:4.4), dicamba plus 2,4-D plus mecoprop (4.2:11:3), MCPA amine, MCPA-K, MCPA-Na, and metribuzin), caused no more than a 20% reduction in C.g.m. spore germination, and appressorial formation was not significantly reduced except by benazolin and metribuzin. Cyanazine and dicamba at recommended rates increased appressorial formation without reducing germination compared to the control. At lower concentrations, the other herbicides recommended for broadleaf weed control (2,4-DB, bromoxynil, bromoxynil plus MCPA (1:1), dichlorprop plus 2,4-D (1:1), imazethapyr, linuron, and picloram) were less toxic to C.g.m. spores. The fungicide triadimefon at recommended rate had no effect on C.g.m. spores. Dicloran reduced germination more than 50% at recommended rate and growth was distorted. At recommended rates, spore germination was inhibited by more than 90% with benomyl, carbathiin, chlorothalonil, iprodione, mancozeb, and thiophanate-methyl although germination increased as concentration declined. Spore germination was totally inhibited at all concentrations with ferbam, thiram, and captan. Exposure to the adjuvants—Agral 90, Alkasurf-0P-10, Atplus-555, Citowett Plus, Enhance, Renex 36, Triton XR, and X-77–inhibited C.g.m. spore germination and reduced spore production compared to the control. Spore germination was significantly higher in suspensions containing ammonium sulfate, Assist, Bio-veg, CD-407, and Tween 20, as well as with starch, sucrose, and water (control) than with the other adjuvants. Spore production was higher in suspensions containing starch and Bio-veg than in those with water and the other adjuvants.

Effects of Selected Herbicides on the Germination and Infection Process of Puccinia lagenophora, a Biocontrol Pathogen of Senecio vulgaris

“…This rate is equal to the concentration we used for 2,4-D in the in planta study. In Grant et al (1990) herbicides at concentrations from 0.01 to 2 times the recommended field rate that control broadleaf, grass weeds, and both types of weeds were tested on germination of spores of Colletotrichum gloeosporioides (Penz.) Sacc.…”

Effects of selected pesticides and adjuvants on germination and vegetative growth of Phomopsis amaranthicola, a biocontrol agent for Amaranthus spp.

“…Compatibility of herbicides with fungal biological control agents has been examined to some extent (Khalil et al. , 1985; Grant et al. , 1990a,b; Poprawski & Majchrowicz, 1995; Rayachhetry & Elliott, 1997; Wyss & Müller‐Schärer, 2001).…”

Innovative Applications of Microbial Agents for Biological Weed Control

“…malvae resulted in enhance efficacy when compared to the application of the mycoherbicide alone (Grant et al, 1990b). More than 50% of the herbicides applied at 0.1 to 2 times the recommended rate did not interfere with the growth of the mycoherbicide (Grant et al, 1990a). However, a study on pesticide and adjuvant compatibility with Chondrostereum purpureum showed that the majority of chemical pesticides (fungicides, insecticides, and herbicides) and adjuvants were fungitoxic to the mycoherbicide at 0.01 and 0.1% (v/v) concentrations (prasad, 1994).…”