Control of Texas Gourd,Cucurbita texana, withFusarium solanif. sp.cucurbitae

The soil-borne fungus,Fusarium solani(Mart.) App. & Wr. f. sp.cucurbitae, has shown potential as a mycoherbicide to control Texas gourd. Formulations and times of application that effectively controlled Texas gourd were determined in field studies. Aqueous conidial suspensions (1 × 108microconidia/ml) were applied preplant incorporated, postemergence, or both at 280 L/ha alone or combined with trifluralin at 1 kg ai/ha. Alginate granules containing fungal spores and hyphae and amended with 2% (w/v) soyflour were applied pre- or postemergence at 220 kg/ha alone or sequentially with conidial applications. Mortality of 70% or greater was achieved with eight of nine fungal treatments. The fungus applied as conidia combined with trifluralin, as well as trifluralin alone, significantly reduced Texas gourd emergence.

Toxicologic Response in Mice Fed Cucurbita Fruit

Reports from Australia of illness in consumers eating bitter squash prompted a 10-wk mouse-feeding study containing increased levels of the fruit of two cultivars of Cucurbita pepo, L., ‘Blackjack’ and ‘Straightneck’, and an accession of the bitter species, Cucurbita texana, Gray, was conducted. The latter produced poor growth, severe diarrhea, anemia and 40% mortality in mice fed diets containing 1% freeze-dried fruit. Diets containing 10 or 20% C. texana caused 100% mortality within a few days. The cultivar contained 3.56 and 1.39 mg per g of fresh fruit cucurbitacins E glycoside and I, respectively. The cultivars of C. pepo, ‘Blackjack’ and ‘Straightneck’, contained no detectable cucurbitacins; animals fed up to 20% freeze-dried squash in their diets showed no toxicity, with normal growth and hematology.

Texas Gourd (Cucurbita texana) Control withFusarium solanif. sp.cucurbitae

An indigenous soil-borne fungus was isolated from infected seeds and seedlings of Texas gourd [Cucurbita texana(A.) Gray] and evaluated as a mycoherbicide. The pathogen was identified asFusarium solaniApp. & Wr. f. sp.cucurbitaeSnyd. & Hans. OnlyCucurbitaspecies were susceptible in host range tests. Ample quantities of microconidia for greenhouse and field plot inoculum were produced in shake culture on Richards' solution. Granular inoculum for field plot tests was produced in 5% (w/w) cornmeal/sand medium. In controlled-environment experiments, inoculated Texas gourd seedlings were killed over a range of air temperatures from 16 to 40 C. Optimum air temperature for disease development was 26 to 30 C. Complete kill of 4- and 8-cm-tall seedlings was achieved after 3 weeks when sprayed until runoff with a microconidial suspension containing 2.0 × 106spores/ml. Texas gourd seedlings were effectively controlled in field plots (99% maximum) with liquid or granular inoculum. Soil samples from infested plots indicated that the fungus persists up to 12 months in a fine sandy loam, but after 12 months inoculum levels were insufficient to cause disease on seedlings grown under optimum conditions for disease development.

Germination of Texas Gourd (Cucurbita texana) and Its Control in Soybeans (Glycine max)

Storage of intact Texas gourd [Cucurbita texana(A.) Gray] pepos for 21 days after harvest increased germination of seeds from pepos collected 15 to 47 days after flowering. Germination increased as day length decreased and as osmotic potential of germination media increased. Temperatures of 20, 25, and 30C resulted in 72, 93, and 99% germination, respectively. No seeds germinated at 10 or 40C. Seedling emergence decreased as planting depth increased, with no emergence from 12.5 cm. Control of Texas gourd in soybeans [Glycine max(L.) Merr.] was achieved with preemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metribuzin plus alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide], and oxadiazon [2-tert-butyl-4 (2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], with successful control partially dependent on soil and climatological conditions. Postemergence treatments that resulted in adequate control included applications of acifluorfen {5-[2-chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoic acid}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene], and metribuzin plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at an early soybean growth stage and repeated.