Cucurbits (squash, cukes and melons) are popular garden veggies. That is probably why questions about cucurbits are second only to tomatoes when it comes to problems that gardeners encounter.
A common question is why aren't plants getting any squash even though they have a lot of flowers? It is important to know that cucurbits have separate male and female flowers. Only the female flowers can produce fruit, and only the males produce the pollen. The cucurbits depend primarily on honeybees to transfer the pollen from the male flowers to the females.
In order for pollination to occur, male and female flowers must be open at the same time. Typically, cucurbits produce all male flowers at the start of flowering, and a little later also produce female flowers. Conversely, plants of hybrid cucurbits generally produce female flowers first and male flowers second. However, before long, both sexes of flowers are open at the same time and then the bees must go to work.
Once male and female flowers are blooming, there are several reasons that fruit still may not develop. Lack of honeybees or low bee activity because of hot weather, wind or rain can hamper successful pollination.
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If the honeybee population is low or nonexistent, assume the duties of a honeybee. Do this by picking a freshly open male flower (they have pollen in the center) and removing the petals, leaving the center portion (anthers) with the pollen. Insert this into the center of a newly open female flower (has a baby fruit at its base). Gently move the anthers around to transfer the pollen from the anthers to the center structure (stigma) in the female flower.
Another common cucurbit question is when gardeners discover small to large dry whitish or tan spots on the leaves of squash, melons or cukes. It is typically most severe on the plant's larger, older leaves and not evident on the youngest leaves. It looks like a disease problem, but it usually is wind injury. This occurs when the wind buffets the leaves about, causing the spiny surfaces of the leaves and stems to wound themselves. Badly injured leaves will be brittle and often tear after more windy weather. Placing a garden in a less exposed spot or shielding the plants from wind might help.
Gardeners also wonder why squash leaves wilt during the day and then perk back up in the evening. Is it a wilt disease or squash bugs? No, this daytime wilting indicates that the leaves are not being supplied with enough water to keep up with the amount of water they are losing through their leaves during the heat of the day. This lack of water may be caused by too little soil moisture, a poorly developed root system, root rot from too much water or poor drainage, or root damage from enthusiastic weed cultivation. Consider the situation and try to remedy it for a healthier, more productive plant that does not wilt during the day.
Other common problems to look for on cucurbits are squash bugs and powdery mildew. You can find out more about these on the Washington State University website called "Hortsense," short for Horticultural Sense at http://pep.wsu.edu/hortsense/.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.