A fungal pathogen, Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. malvae, isolated from anthracnose symptoms of round-leaved mallow (Malva pusilla Sm.), was shown in greenhouse tests to be host specific to Malva spp. and velvetleaf (Abutilon theophrasti Medic. #3 ABUTH), and only with slight attack on hollyhock [Althaea rosea (L.) Cav. # ALGRO], Malope trifida Cav., and Venice mallow (Hibiscus trionum L. # HIBTR). Round-leaved mallow plants inoculated with a spore suspension of the fungus were killed after 17 to 20 days. It was less pathogenic on velvetleaf with 60 to 70% attack. The fungus can readily be cultured and field tests from 1982 to 1987 resulted in excellent control of round-leaved mallow under natural conditions. Therefore, it has good potential for biological control of round-leaved mallow in field crops.

Tolerance of strawberry to Colletotrichum gloeosporioides f. sp. malvae, (C. g. malvae) a mycoherbicide for control of round-leaved mallow, was tested in the growth chamber and field in an area infested with round-leaved mallow. No visual infections of C. g. malvae were observed on inoculated strawberry plants in the growth chamber or field. However, C. g. malvae was reisolated from inoculated leaves and petioles from both situations, but no adverse effects were observed on strawberry plant development in the growth chamber or on berry yield in the field. Round-leaved mallow competition was detrimental to strawberry establishment, and berry yield was reduced by half compared to weed-free plots. In round-leaved mallow infested plots, treatment with C. g. malvae resulted in more vigorous strawberry plants, with berry production almost to the level of weed-free. Therefore, use of this mycoherbicide for control of round-leaved mallow in strawberries is a viable option that fits well in an integrated pest management system.

In four tests conducted in 2 years, Alternaria cassiae Jurair and Khan effectively controlled sicklepod (Cassia obtusifolia L. ♯ CASOB) as indicated by stand counts of the weed and by soybean [Glycine max (L.) Merr.] yields. The number of sicklepod seedlings was reduced more than 90% within 14 days after foliar applications of A. cassiae conidia were banded (46 cm) at rates of 4.2 and 2.1 kg/ha (9.4 and 4.7 kg/ha broadcast, respectively). One banded application of 0.04 or 0.4 kg/ha (0.09 or 0.9 kg/ha broadcast, respectively) did not satisfactorily control sicklepod. These results indicate that sicklepod control may be enhanced by multiple applications of A. cassiae.

In greenhouse studies, Fusarium lateritium Nees ex Fr. was effective in suppressing the growth of velvetleaf (Abutilon theophrasti Medic. # ABUTH) and prickly sida (Sida spinosa L. # SIDSP). Sprays containing conidia of the fungus and fungus-infested sodium alginate-kaolin clay granules controlled both weeds in corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybeans [Glycine max (L.) Merr.] without causing a reduction in dry weight of the crops. In field tests, postemergence foliar applications of the fungus controlled velvetleaf and prickly sida 40 and 80%, respectively, in 1982, but controlled only 27 and 34% of velvetleaf and prickly sida, respectively, in 1983. Preemergence applications of the fungus in the granule formulation controlled velvetleaf and prickly sida 46 and 59%, respectively, in 1982. In 1983, this treatment controlled the weeds 35 and 38%, respectively.