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WHAT’S WRONG WITH MY CUCURBIT?

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published- JUNE 27, 2014

WHAT’S WRONG WITH MY CUCURBIT?

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 in their vegetable gardens.

A common question is, ‘why aren’t I getting any squash even though my plants have a lot of flowers?’ To understand the answer 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 needed for pollination and fruit development. The cucurbits depend primarily on honeybees to transfer the pollen from the male flowers to the females.

In order for pollination to occur, both 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 at the same time, there are several reasons that fruit still may not develop. Lack of honeybees or low bee activity due to hot weather, wind, or rain can hamper successful pollination.

If the honeybee population is low or nonexistent, you can 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 comes from area gardeners when they 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 winds buffets the leaves about, causing the spiny surfaces of the leaves and stems to wound themselves. Badly injured leaves will be very brittle and often tear after additional windy weather. Placing a garden in a less exposed spot or shielding the plants from wind in some way might help.

Area gardeners also wonder why the leaves of squash 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 WSU website called ‘Hortsense,’ short for Horticultural Sense. You can find Hortsense at http://pep.wsu.edu/hortsense/. Start looking for squash bugs now.

Published: 6/27/2014 11:40 AM

IT ISN’T WHAT YOU THINK IT IS

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published- JULY 11, 2014

IT ISN’T WHAT YOU THINK IT IS

I recently overheard a woman in a local store asking for a spray to kill the little green worms on her lettuce. I had to restrain myself from offering her unsolicited advice. I too had just found ‘little green worms’ on my lettuce, but I recognized them as syrphid fly larvae.

Syrphid flies are also known as hover flies or flower flies because they are usually noticed when hovering over flowers. They may cause alarm because they have a black and yellow striped body, resembling a bee or wasp. However, syrphid flies are benign and do not sting or bite.

The adult flies eat flower pollen and nectar. They are also valuable pollinators. You should not be afraid when you see a syrphid fly hovering around your garden plants, but any aphids present should be very afraid. That is because many types of syrphid flies are predaceous. These syrphid flies lay their eggs near colonies of aphids. The eggs hatch into hungry larvae that will eat hundreds of aphids in a month.

If you see a ‘little green worm’ on a plant infested with aphids, take a close look. Syrphid fly larvae have a tapered body with no legs. They blindly move over the leaf surface searching for aphids to eat. When they find one they use their piercing mouth to suck out its body fluids.

So if you find a little green worm on your lettuce or see a bee-like fly hovering around your flowers, it is likely a sphyrid fly larva or adult. Syrphid flies are beneficial insects that do double duty, eating aphids and helping with pollination. Encourage them instead of buying a spray to kill them.

For much more information about ‘Beneficial Insects, Spiders, and other Mini-Creatures in Your Garden – Who They Are and How to Get Them to Stay’ go to http://cru.cahe.wsu.edu/CEPublications/EM067E/EM067E.pdf for your free downloadable copy of this outstanding and fascinating publication written by Dr. David G. James, Associate Professor, WSU Department of Entomology.

Several local gardeners have come to me recently because they were worried about the silvery patches on the leaves of their zucchini plants. They wondered if it was powdery mildew, a fungus disease that is fairly common in area gardens. It first shows up as small white powdery spots on squash leaves. These spots grow larger until the fungus covers the entire leaf and stem, killing the infected tissues It typically shows up on squash late in the growing season, about the time the plants are finished producing fruit.

Luckily, what these gardeners have encountered is the natural silvery blotchy variegation characteristic of some zucchini cultivars (varieties). It is not a problem and the plants are healthy for now, but it is advisable to watch for signs of powdery mildew on squash, cukes, and melons.

If you have had problems with powdery mildew on your squash before, you may be able to avoid it by doing a few simple things. When possible, plant cultivars that indicate they are resistant to powdery mildew. Don’t plant your squash or other cucurbits where they will be in the shade of other plants or structures for part of the day. Provide good air circulation by not crowding the plants. Finally, rotate your crops so cucurbits are not planted in the same location for at least two years. For more information on powdery mildew go to WSU’s Hortsense Website at: http://pep.wsu.edu/hortsense.

Published: 7/11/2014 11:39 AM

ROSES, APHIDS, AND POWDERY MILDEW

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

Last week we talked about when and how to prune roses. Since spring is right around the corner, now’s a good time to talk about the two rose problems that local gardeners often face… aphids and powdery mildew.

APHIDS: Aphids are small green or pinkish soft-bodied insects found in clusters on succulent new bud and stem growth. The aphids suck sap from the plant. When they’re present in high numbers, they damage growth. Rose aphids overwinter as eggs on buds and stems, emerging at the same time that new growth begins in the spring.

Horticultural oils can be used to help minimize aphids problems by smothering aphids eggs before the young aphids emerge. The oils are applied at the delayed dormant stage, when the buds start to emerge.

There are other least-toxic ways to discourage the buildup of aphid infestations on roses. Avoid excessive or unnecessary applications of nitrogen fertilizer. The nitrogen promotes vigorous, succulent growth where aphids like to feed. Using a slow-release or low nitrogen fertilizer can avoid lush early-season growth.

Another non-chemical option for managing aphids is water. A strong stream of water can be used to wash aphids off rose leaves and stems. Spraying roses regularly with water is an easy way to keep aphid populations down.

If these methods fail, there are a number of organic and inorganic pesticides for aphid control. The easiest to use are the systemic insecticide products that are mixed with water and applied to the soil for uptake by the roots. The Bayer Advanced product line includes several soil-drench products containing imidacloprid for use on roses.

POWDERY MILDEW: Powdery mildew is a fungus disease characterized by a white powdery coating on leaves and buds. You can minimize powdery problems by not encouraging succulent growth which is most vulnerable to infection by powdery mildew. Also, sprinkling plant leaves with water helps by washing spores off the plant.

One new ‘organic’ spray that gardeners have been reading about for control of powdery mildew is milk, yes the stuff that comes from a cow. However, while this recommendation has appeared in various gardening publications, Linda Chalker-Scott, WSU Extension Horticulturist, points out that there have been no published scientific studies investigating the use of milk to prevent powdery mildew on roses or other ornamental plants. There have been studies on the effectiveness of milk spray applications for the control of powdery mildew on melons, cucumbers, and squash. These studies indicate that whole milk does provide some control of powdery mildew.

Chalker-Scott notes that the only anecdotal evidence, not scientific research, indicates that milk is effective in controlling powdery mildew on roses. She also points out the drawbacks of using milk for powdery mildew prevention include the unpleasant odor of the milk fat as it breaks down, the growth of benign fungal organisms that colonize the leaves as part of the break down process, and that milk may only be effective if it’s applied prior to powdery mildew developing.

With those drawbacks, you may prefer to use an organic or inorganic fungicide for control of powdery mildew on roses Most of these require frequent (every seven to ten days) application to protect new growth as it develops. However, tebuconazol can be applied as a soil-drench for uptake by the roots. Several Bayer Advanced rose care products contain both tebuconazol and imidacloprid, providing aphid and powdery mildew control for ‘up to six’ weeks. These products are a bit pricey, but they avoid the risk of spray drift and don’t require spray equipment or frequent re-application.
Published: 3/9/2012 11:33 AM

POWDERY MILDEW ATTACKS PLANTS

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

I can’t believe all the powdery mildew in my garden this fall. It’s all over… on summer squash, zinnias, coreopsis, purple coneflower and even my Wave petunias! It’s easy to identify powdery mildew with the characteristic white powdery patches of mycelium on the top surface of leaves and stems.

While often referred to in the singular, powdery mildew is not just one fungus disease, but it’s actually several different closely related fungi. A specific powdery mildew fungus will only attack a specific species or specific plant family.

Area gardeners are lucky when it comes to plant-attacking fungal diseases. Most fungal diseases require the presence of free water on plant tissues for an infection to occur. Our arid climate on this side of the Cascades makes it easier to garden because our plants are troubled by few fungal diseases.

Powdery mildew is an exception. It doesn’t need free water for infection, just high humidity. For infection to occur, mildew spores must be present on a susceptible plant along with the right conditions for infection to occur. High humidity, poor air circulation, moderate (60 to 80 degrees) temperatures, and shade are all favorable conditions for powdery mildew infections.

I’m seeing so much powdery mildew now because the weather has cooled off and the humidity is probably higher. Also, my container garden plants are very crowded. In addition, I fertilized the plants in mid-August, stimulating newer, younger growth that’s more susceptible to attack. Plus, some of my planters only get sun for part of the day.

So how worried am I about all this powdery mildew? Not much. It’s late in the season and the annual flowers and vegetables will be gone with the impending hard frost. Applications of fungicide would be wasted. However, I am planning on taking steps to avoid it next year.

First, a thorough garden clean-up is planned. It’s important to remove and dispose of all infected plant material from the garden. (Composting will not kill all the fungus, so these plants will go into the garbage .) If I leave the infected dead plants and debris in my garden, it would be a source of spores for reinfection next season.

To improve air circulation next year, I’ll try to refrain from “over planting” my container gardens. That will be difficult since I love crowded containers overflowing with plants. I also plan to watch mildew prone plants, like zinnias, and may consider applications of fungicide if the disease appears early in the season.

It’s important to note that many garden fungicides only work as protectants, protecting new plant growth from getting powdery mildew, not killing it on already infected parts of the plant. There are a few garden fungicides, such as plant oils, that work both as protectants and eradicants, killing the disease on plants with mild infections. They won’t kill the disease on heavily infected plants, like the ones in my garden this fall. If powdery mildew is a recurring problem on woody or perennial plants in your garden, you should plan on applying protectant fungicides before the disease appears each year.

Go out in the garden today and check your plants. You might find evidence of a powdery mildew attack too.

Published: 10/3/2009 10:57 AM

OUT IN THE GARDEN – POWDERY MILDEW AND LAVENDER

written by Marianne C. Ophardt WSU Extension Faculty for the Tri-City Herald, Kennewick, WA I was out in the garden this week to ‘dead head’ or remove the spent blossoms from my roses. Conventional wisdom says you should prune off these dead flowers by carefully pruning back to a five-leaflet leaf. When you have a number of rose bushes, this gets to be a tedious, time consuming chore and many summers went undone in my garden. Last year, I decided to take an easier approach using a little electric rechargeable hedge trimmer. I now use it to quickly trim off the dead flowers from my roses and shrubby perennials. After using the hedge trimmer, the re-bloom on my roses late last summer was better than ever. However, I’m not sure how good it will be this year. While ‘buzzing’ off the dead blooms, I noticed that my roses have more powdery mildew than other years. Other local gardeners have also been noticing this problem on their roses too, as well as on other plants that are susceptible to powdery mildew, such as cherries, grapes and sycamores. Powdery mildew is a group of similar fungi that attack plants. The tell tale sign of powdery mildew infected plants is the grayish white ‘powdery’ coating on green leaves, stems, and fruit. Severe infections are very evident with a thick white coating but moderate to mild infections are less apparent. Infected tissues tend to become stunted and leaves are usually curled or distorted. Infected areas may turn brown to black later in the season. The skin of infected fruit, such as apples and grapes, becomes leathery or ‘russeted.’ Unlike many fungus diseases that attack plants, powdery mildew does not need wet conditions to spread and infect plants. The powdery mildews are favored by humid conditions when the days are warm and the nights are cool. Infections are most severe where plants are crowded and have poor air circulation. Infections are also worse in moist, shady areas of the garden or landscape. Powdery mildew primarily infects immature succulent growth, so susceptible plants that are watered and fertilized heavily are top candidates for infection. Knowing what conditions favor powdery mildew is a good guide to managing the disease. Not crowding plants and pruning to ‘open them up’ to allow for good air circulation can help. This year, I didn’t prune as many canes off my roses as usual and the shrubs are quite dense. Next year, I can lessen the mildew problem by leaving fewer canes when I prune in the spring. It’s also important not to create lush vegetative growth by applying too much water or fertilizer. In the fall, rake up and dispose of the fallen leaves from infected plants. During the winter, prune out and dispose of severely infected canes or branches. Surprisingly, another way to manage a powdery mildew infection is by thoroughly wetting the surfaces of leaves and stems of infected plants two or three times a week. This washes some spores off the plant and it also destroys other spores by causing them to burst. If possible, do this early in the day. The best way to avoid problems with powdery mildew is to plant resistant varieties. Certain varieties of plants are more susceptible to the disease than others. You are much further ahead to plant resistant varieties of roses, grapes, sycamore, and others. There are some fungicides that can be used for mildew control when an infection is severe and the other methods haven’t worked. However, these aren’t needed during the summer when higher temperatures usually hold it in check. If you feel you need a fungicide for control, apply it earlier in the season and follow label directions. Repeated applications usually will be needed to protect new growth as the plant grows. While checking out the garden, I also noticed that the lavender was just about done blooming. I adore lavender. You can’t go wrong with this shrubby perennial. It’s a member of the mint family and is native to the Mediterranean region. It prefers well-drained, slightly alkaline soil. It’s easy to grow. It needs little water once established, it likes the heat, and it has few insect pests. However, it must have full sun and good air circulation. There are at least 20 species of lavender, but the most commonly grown garden species is English lavender, Lavendula angustifolia. It’s a hardy shrubby perennial, growing from one to three feet in height. The leaves are typically narrow. There are many very nice purple cultivars (varieties) of English lavender, but there are also a few white and pink ones too. Some of the cultivars popular with gardeners are Hidcote, Munstead, and Twickel Purple. Irene Doyle is favored for its ability to flower twice during the season. Lady was a 1994 All-America Selection that can be planted from seed and flowers the first year. Some of the Lavandin lavenders (Lavendula x intermedia) are also popular. These are hybrids between English lavender (L. Angustifolia) and Spike lavender (L. latifolia), a tender type grown primarily for its essential oil. The plants and leaves of Lavandin cultivars tend to be larger than those of English lavender and have a more pungent fragrance. Grosso grows to five feet across when in flower. Two other popular Lavandin cultivars are Provence and Hidcote Giant. Of course, there are many more cultivars that intrigue gardeners who love lavender. While lavender is an easy care plant, a little light pruning improves its looks and performance. In early fall you will want to cut back the plants a bit, not so far as to cut into woody stems, leaving one or two inches of green. Then in the spring you prune heavier, cutting back the plant from 1/3 to 1/2 of its size, and still leaving several inches of green above the woody stems. This may seem drastic but it stimulates new growth and results in a denser, more compact ‘shrub.’ Seeing the lavender reminds me that this weekend is the annual Sequim Lavender Festival where lavender enthusiasts can visit beautiful lavender farms, buy lavender products from vendors, and take in the lovely sights and aromas of the ‘Lavender Capital of North America.’ They expect over 30,000 to attend. Whew! If you don’t like such big crowd, think about visiting our local lavender growers and buying their products. ‘Lavender’s R Us’ even holds a lavender festival in June in Dayton and encourages visits to their Waitsburg store. Some of the lavender growers in our region are: Lavender

s R Us, Robin Thomas, Waitsburg, WA 337-9020 Lavenderthyme, Susan Bunnell, Prosser WA, 973-2855 Blue Mountain Lavender Farm, Karen Grimaud, Touchet WA 529-3276

Published: 7/16/2005 11:45 AM

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