Exploring Cover Crops in an Integrated Approach to Reduce Disease Pressure and Increase Beneficial Insects in Watermelon Production

View the project final report

Commodities

• Fruits: melons

Practices

• Crop Production: cover crops, pollination
• Pest Management: integrated pest management

Cover crops offer a range of benefits that include suppressing disease in subsequent cash crops, providing habitat for beneficial insects, and promoting pollinators. Overwintering cover crops can provide early floral resources for pollinators and refuge to other beneficial insects like natural predators before cash crops are planted. These attributes may help bridge beneficial insects into the crop following cover crop termination.

Cover crops have also been found to reduce severity of some watermelon diseases. Based on these benefits, it is worthwhile to investigate the potential of different cover crops for use as an integrated pest management strategy in watermelon production. Such a strategy would benefit watermelon yield while cutting costs and pesticide use, making production more sustainable. The grant provided funding for 1-year of this research project designed to determine the cover crop monocultures or mixtures best suited for the watermelon disease suppression, pollinator production, and bridging beneficial insects into watermelon production systems.

To achieve this goal, insects  were sampled in various cover crop treatments before termination and after termination before planting watermelon. Disease and insects were evaluated in the subsequently planted watermelon. Pollinators were sampled in the cover crops and watermelon during bloom as well. Findings were presented to watermelon growers during talks and at field day watermelon workshops. 

An important finding from this research was that when compared to the control with no cover crops, none of the winter cover crops investigated were found to increase major watermelon pests or disease. In general, cover crops that flowered including the mustard, crimson clover, and pea attracted more beneficial insects. These cover crops also hosted aphids that served as a food source for beneficial insects like lady beetles and parasitoid wasps. Although these aphids were present in the cover crops, they were not bridged into the watermelon because they were not melon aphids. The grass cover crops tended to support fewer insects and often fewer pests compared to the control, however, outbreaks of rice stink bugs occurred and were found to be more prevalent in the grasses. Because there were insects present before and after cover crop termination, a bridging effect likely occurred. The bridging effect was not very clear because pest pressure was low in the watermelon. Most of the beneficial insects in the cover crops were natural enemies of aphids like lady beetles and parasitoid wasps. Because melon aphids were not abundant in the watermelon, there was no food source for the natural enemies, which may explain why they were not very common in the watermelon either.

It was difficult to determine whether the cover crops impacted watermelon disease because fungicides were applied in order to ensure that their yield was preserved as part of a larger project investigating the effects of cover crops on watermelon. Disease incidence was consequentially low and was the same across all treatments in the field. In order to determine the true effects of cover crops on watermelon disease, it might be necessary to perform a more controlled study in which the plants are inoculated with the pathogens. It is important to note that none of the cover crops bridged diseases into the watermelon.

Pollinator sampling revealed that native bees played a very important role in watermelon pollination. Cucurbit specialists were very common throughout the field, much more so than honey bees. Sampling in the cover crops revealed that only those that flower before termination serve as resources for pollinators. Mustard was one of the cover crops to flower before termination. However, when canola and Austrian pea were permitted to grow until bloom, they also supported bees that had emerged in the spring. Depending on fall planting date and winter weather conditions, other flowering cover crops may have potential to flower before termination and provide early season resources for bees as well.

Based on the findings of this project, growers that seek to promote pollinators should plant a flowering winter cover crop like mustard or canola that blooms before termination in the spring. If growers would like to keep general agricultural pests low, then they should use a grass cover crop like black oats, cereal rye, or wheat. If melon aphids are an issue, growers should plant mustard or a legume to increase natural enemies of aphids. It is also important for growers to know that if they are growing a legume nearby they should avoid using legume cover crops because they could increase problematic pests like pea aphids. If growers are going to be producing cereals, then they should avoid grass cover crops that were shown to support rice stink bug. Ultimately, growers should choose cover crops not only based on their potential impact on beneficial insects but also based on other benefits like nutrient contribution and their impact on soil health and yield. 

Objective 1: Evaluate winter cover crops and cover crop mixtures to determine which are best suited for increasing natural enemies.

Objective 2: Evaluate winter cover crops and cover crop mixtures to determine which are best suite for disease suppression in watermelon.

Objective 3: Determine the effect of different winter cover crops and cover crop mixtures on pollinator abundance and diversity, especially for pollinators essential to watermelon production.

Objective 4: Participate field days  to disseminate information on cover crops in watermelon production systems.