- Vegetables: cucurbits
- Crop Production: cover crops, no-till
- Education and Training: demonstration, extension, workshop
- Natural Resources/Environment: soil stabilization
- Pest Management: allelopathy, biofumigation, cultural control, mulching - plastic, soil solarization, trap crops
- Production Systems: agroecosystems
- Soil Management: green manures, soil physics, soil quality/health
Root-knot (Meloidogyne incognita and M. javanica) and reniform (Rotylenchulus reniformis) nematodes are major plant parasites in cucurbit cropping systems in Hawaii. This “Cover crop 5-in-1 Approach” project, as the name suggests focused on utilizing 5 mechanisms that Brassica cover crops (Brassicaceae) employ to combat the plant-parasitic nematodes. The mechanisms included poor or non-host effect, trap crop effect, biofumigation effect, host plant tolerance due to green manure effect, and enhancement of soil-borne nematode antagonistic microorganisms. During this 2-year project, 4 greenhouse and 7 field experiments were conducted. Two greenhouse experiments examined susceptibility of ‘Caliente 199’ brown mustard (Brassica juncea) and ‘Sodbuster’ oil radish (Raphanus sativus) to the nematodes. Brown mustard was a good host of M. incognita and R. reniformis whereas oil radish was a poor host of M. incognita but good host of R. reniformis. Based on greenhouse trials, M. incognita or R. reniformis eggs required 465 degree-days (DD) or 512 DD, respectively to reach egg-laying females on brown mustard and oil radish. With a daily average of 22°C at 4-inch soil depth in Hawaii, these results could mean M. incognita or R. reniformis eggs can complete a life cycle on the Brassicas in 5 or 6 weeks, respectively. Thus, Brassica cover crop should be terminated 5-6 weeks after planting to avoid further nematode reproduction. In the field, when oil radish was grown for 6 weeks, it did not reduce soil populations of both root-knot and reniform nematodes. However, when brown mustard was grown for 5 and 6 weeks, it reduced numbers of root-knot nematodes but not when grown from 7 weeks. Conversely, reniform nematode was reduced when brown mustard was grown for 7 weeks. These results indicated that brown mustard was a good trap crop of both nematodes but the trap crop effect cannot be predicted by DD, unlike what we had hypothesized.
Biofumigation effects of the Brassicas on the nematodes were assessed 1 week after soil incorporation of above-ground biomass and at monthly interval after a zucchini (Cucurbita pepo) crop was planted in multiple field trials. Overall, oil radish failed to suppress both root-knot and reniform nematodes but increased bacterial feeding nematodes and nematode enrichment index (EI) indicative of nutrient enrichment, a clear demonstration of green manure effect. Whereas biofumigation with brown mustard suppressed root-knot nematodes in three replicated trials and suppressed reniform nematode in one of the three trials. Bacterial feeding nematode population and EI were transiently increased for up to 1 month after brown mustard biofumigation. Among all these field trials, we consistently found that biofumigation against plant-parasitic nematodes was most effective when aerial tissues were macerated and tilled followed by covering the soil with black plastic mulch. The results were confirmed by significant increase in soil glucose and sulfate concentrations, the by-products of biofumigation besides isothiocyanates. During these studies, we also found that although both sulfate and glucose in the soil were negatively related to the targeted nematodes based on canonical correspondence analysis, sulfate was a better indicator of biofumigation effect as it had a stronger negative relationship with plant-parasitic nematodes and it is more stable in the soil for analysis.
This project examined the mechanisms of Brassica cover crops employed to manage plant-parasitic nematodes including 1) biofumigation effects that is toxic to plant-parasitic nematodes; 2) trap cropping effect that allows nematode infection but also making them more vulnerable to allelopathic effect of biofumigant; and 3) green manure effect that improves plant tolerance to nematode damage. Our goal was to maximize the benefits of Brassica cover crops by integrating biofumigation with different plastics or through mixed planting of brown mustard (Brassica juncea) and oil radish (Raphanus sativus) cover crops. Plant-parasitic nematodes targeted in this project were root-knot nematodes (Meloidogyne incognita and M. javanica) and reniform nematode (Rotylenchulus reniformis).
The overarching goal was to develop biofumigation method suppressive to plant-parasitic nematodes and yet beneficial to soil health for cucurbit crop production.
Specific objectives of this project were to:
- Examine susceptibility of ‘Caliente 199’ brown mustard and ‘Sodbuster’ oil radish to root-knot (Meloidogyne incognita) and reniform (Rotylenchulus reniformis) nematodes.
- Determine heat-units required by incognita and R. reniformis to reach egg-laying females on ‘Caliente 199’ brown mustard and ‘Sodbuster’ oil radish;
- Compare ‘Caliente 199’ brown mustard and ‘Sodbuster’ oil radish for their biofumigation effects against plant-parasitic nematodes and soil health improvement benefits;
- Determine best biofumigation method suppressive to targeted plant-parasitic nematodes;
- Determine best biofumigation indicator for assessing suppressive activities on plant-parasitic nematodes;
- Compare black plastic and clear solarization mulch for their ability to enhance biofumigation effects on plant-parasitic nematodes;
- Examine biofumigation effects on free-living nematodes as indicators of soil health.