By Drs. David Gonthier and Ric Bessin, Department of Entomology, University of Kentucky

 

The idea is simple. Cover your crops with a fine-mesh netting that limits pests and you will reduce insect damage to your crops. Our research over the years has demonstrated that protective netting barriers are extremely effective at limiting pests of squash and melons and is a viable pest control strategy for many growers, and especially those working in organics. See a previous blog post for a description of the mesotunnel systems we study. But as with many promising pest control solutions, there are challenges and trade-offs. With the case of mesotunnels on squash and melons, managing pollination is one such challenge.

 

Most cucurbit species, like muskmelon and acorn squash, are entirely dependent on insects to pollinate their flowers. Meaning in order for fruit to successfully develop, an insect must visit each female flower and deposit pollen. Without this, squash and melons fruits will abort, never fully develop, or have severe deformities that make the fruit unmarketable. Our previous research suggests that a number of bee species make great pollinators of squash and melons including bumble bee species and squash bees.

 

The major challenge of course is that covering your cucurbit crops with a fine mesh insect net to limit access to pests also limits access to pollinators! When the plants begin to flower, there will be no pollinators to pollinate flowers and fruits will never develop. For this reason, we have been studying a variety of strategies to improve or maintain pollination within these mesotunnel systems.

 

On-off strategy

First, given that damage by insect pests, such as cucumber beetles and squash bugs, is highly damaging early in the growing season when cucurbit plants are small, the most traditional deployment of the fine mesh netting is at the beginning of the season to protect young plants. The nets are then removed from the crops once the plants begin to show female flowers, allowing wild or managed pollinators to visit flowers. In this case, the nets are never re-deployed. This method, of course, doesn’t protect the plants after flower set and therefore we do not always see great success. It may be necessary to spray insecticides to manage pests after the nets are removed.

 

On-off-on strategy

Second, we can deploy the netting barrier early on, then take it off at the flower stage, and then once flowering has been completed (about two weeks later), we return the nets back over the cucurbit crops. Similar to the on-off strategy, this on-off-on strategy protects transplants early on when they are most vulnerable, but allows wild pollinators to visit flowers before the nets are redeployed after flowering to protect the cucurbits as fruits develop. But there is the danger that pests will also  access the cucurbits while the nets are off and returning the nets to the field will only trap pests within the barrier. For this reason, it may also may be necessary to spray insecticides right before or right after the nets are put back on the plants once flowering is complete.

 

The stem underneath female flowers is swollen (on left) while male flowers have a thin stem (right).

 

Open-ends strategy (modified on-off-on)

The on-off-on strategy also brings up another interesting question. How much of the net must you remove in order to achieve successful pollination throughout your entire field? Dr. Jean Batzer, a former Assistant Scientist at Iowa State University, developed a method where we open only the ends of the mesotunnels during flowering. Here in Kentucky, we have found successful pollination throughout the entire 120 ft long row cover with this method. Only opening the ends of the mesotunnel also saves a lot of effort because you do not have to undo the long sides of the mesotunnels, saving valuable labor and time. However, the success of the open end strategy may depend on the length of the mesotunnel. Large scale commercial fields may be too long for this method to work well. We hope our future research will help answer this question.

 

Full season strategy (stocked bees required)

Finally, it is possible to stock bumble bee colonies underneath of the mesotunnel nets in order to introduce pollinators during flowering without having to open up the barrier system at all. Stocking bees has proven successful at providing pollination on smaller mesotunnel systems (~30 ft long of 3 rows of cucurbits), but the jury is still out on whether one bumble bee colony can pollinate a larger (100 ft – 300 ft) commercial scale field. Additionally, bumble bee colonies are expensive; One colony can cost roughly $150. The question then becomes, can you get a yield bump big enough to improve profits by more than $150 by stocking bees? We are currently exploring how much acreage can be successfully pollinated by a single bumble bee colony to better understand the merits of stocking bees in mesotunnel systems.

 

As this is the early stages of this research, we don’t have all the answers figured out. And the most cost-effective system varies from year to year. However, working together with economists, horticulturalists, and entomologists, we hope to optimize a sustainable mesotunnel system that harmonizes pollination and pest control while also being highly profitable.