Protecting Melons Against Bacterial Wilt

 

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The number one disease melon growers face is bacterial wilt, a devastating infection that can take out a significant chunk of growers’ crops, explains Celeste Welty, Extension entomologist at The Ohio State University. The only way to control the disease is to control the insect that vectors it, the cucumber beetle.

Although her colleague, Sally Miller, professor of plant pathology, also at The Ohio State University, admits that the insect can be a formidable adversary — vectoring the disease to young plants by chewing and defecating and then moving to another — both say their studies have shown that there are options for organic growers in the form of row covers and trap crops.

Covering Your Bases

Row covers circumvent the conventional use of insecticides by creating a physical barrier between the plant and the insect. “This method has been available to organic growers for years,” explains Welty. “You put the covers on when you transplant, and take them off when the flowers appear for pollination,” she says. “But our study shows that you don’t need to take them off right away, because the first flowers that appear are male. You can wait for the female flowers to appear. At Iowa State University, our colleagues have shown that if you just leave the covers on for 10 days longer than normal, you get significantly better control of bacterial wilt.”

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Although Welty says this process of waiting to remove the cover is controversial because being the first to market is important, she says that because of the lack of options for organic growers, the wait may be worth it if it means a good yield.

For growers wanting to test row covers in their field, Miller offers a few warnings. “If you’re transplanting, the plants can be quite tender and can fry in the heat, so being care-ful of conditions is important.”

Welty agrees, adding, “hardening off is less critical with row covers, though, because the plants are not directly exposed to the elements like wind and rain.” The covers themselves, however, are exposed, so Miller suggests sandbagging or using ground staples to weigh them down to assure they are not pulled off, as the installation process can be quite laborious.

Welty and Miller also emphasize the importance of timing. “We covered our crops the same day we put them out,” says Welty. “This is really important because beetles are known for moving in immediately.”

Furthermore, Miller encourages growers to be sure they are rotating their crops appropriately as to avoid beetles overwintering in the soil and coming up underneath the row covers.

Creating A Distraction

The use of trap crops, the second focus of Miller and Welty’s study, involves distracting the pests with a crop that is more attractive to them. In the case of melons, growers could use squash, a more preferred meal for the cucumber beetle. “This preference is shown with other crops as well,” explains Welty. “For example, studies have shown the diamondback moth much prefers collards to cabbage.”

Welty explains that their study utilized the trap crop around the entire perimeter of the main crop. “Imagine it like a picture frame,” she says. “They’ll go to the outside, become satisfied, and stay there. Once beetles find a host, they don’t usually move around much.”

In order to achieve the optimal level of distraction, both Miller and Welty say that it is ideal to plant the trap crop around two weeks prior to the main crop.

“This way,” explains Miller, “the insects are established on the trap crop before the main crop gets going.”

Welty adds that although it is ideal to plant the trap crop earlier than the main crop, she admits that this can cause logistical difficulties as far as weeding is concerned. “The timing won’t be in sync,” she says, “but planting at the same time can cause direct competition between the two crops.”

As far as how much of a trap crop is needed to get the bugs’ attention, Welty says they planted the squash two rows deep around the entire perimeter. She does say, however, that it might be possible for larger operations to cut costs by planting a few rows every 50 to 100 feet.

“Take your time and be patient with the trial and error process,” says Welty. “Our results with both methods have been promising.”

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