Dear Pam,

You may be right with your diagnosis but it might also be bacterial wilt.  Are there any cucumber or striped cucumber beetles in your garden?  They carry the bacteria and then bite into the plant and transfer the bacteria.

Fusarium wilt should show up in the vine itself.  Look for vascular discoloration or something that doesn't look right when compared to a healthy vine.

First things first, get rid of all the affected vines, in the trash.  Clean all your tools with a 10% bleach solution, dip and let them soak for several minutes.  If you used a pot, clean that with the bleach solution as well.  

Fusarium wilt is a fungus that lives in the soil and plants are infected through the roots.  Check the roots of the diseased plants for damage.  Best options are removal of the soil if it is in a pot or raised bed, second is rotate your crops out of that bed, about 5 years worth, and plant fusarium wilt resistant watermelons in another area.  There are no red fleshed watermelons that are resistant to all of the fusarium fungi.  However, the amount of fungi in the soil drops 20% after the first year without watermelons according to soil scientists.

This disease usually starts in the spring but the wilt does not show up until it gets hot.  And if you never had this issue before it might have come in with the seed or the plant if you purchased a transplant.

Grafting onto a resistant root stock is almost always done to small seedlings.  I do not have a source for grafting plants at this stage of growth.  However, there are grafting videos online and it is not difficult, but it is labor intensive and usually more expensive to have someone else do it.  Evidently gourd plants are resistant to fusarium wilt.  That would be my choice for a graft.

If you do have cucumber beetles, getting rid of them is important.  They lay eggs in the soil, hatch, eat the roots until they pupate and then eat the leaves and the flowers infecting everything.  They will migrate to other plants especially corn this time of year and lay more eggs.  If there are enough of them, they can eat the corn roots to the point that the stocks fall over.  

It is important to keep their population as low as possible as they overwinter in the soil. Disturbing the soil around your plants, spraying with organic sprays (not in the flowers or when the pollinators are there) is important.  Put up yellow sticky cards to attract  and catch them.  And, next season, put up row cover until you need the pollinators, remove the row cover for short periods of time during the day and replace at night.  That keeps their populations down in most gardens.  

Spray with insecticidal soap or 100% Neem oil.  You can make your own.  Insecticidal soap - use Castille soap, 1 tablespoon, 1 tablespoon regular vegetable oil and fill a spray bottle with water, shake and spray.  Pure Neem oil can be found online.  One teaspoon of Neem, 1 tablespoon of oil fill the bottle with water and spray.  Neem will congeal.  Put the bottle in hot water for a few minutes and shake vigorously.  Then measure and mix your spray.  Both sprays will kill pollinators.  Both need to be shaken before spraying and both can be stored until you finish using them.

Another option is bio control.  There are businesses that sell predator insects that will eat both larva and adult insect pests.  Google predator insects and you will see the business listings.

I am attaching a link from Michigan State which also suggests growing a green manure.  This usually a legume pea, vetch, clover that set nitrogen in the soil. They are called green manures because they are green plants and manure because they add nutrients to the soil as manures do. 

Mowing it and leaving it to compost in the soil adds more nutrients. This article is for farming but has significant information on fusarium wilt.  It also has a picture of the stem of a diseased watermelon that you can compare to your plants.

 https://www.canr.msu.edu/news/managing_diseases_caused_by_fusarium_the_case_of_watermelon_wilt 

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