Thursday, July 9, 2020

Hummingbirds and Pollination





 

About 25% of plants are wind pollinated. The rest rely on pollinators: bees, bats, beetles, butterflies and yes, hummingbirds, as well as some other birds. During the day hummingbirds feed about every 10 minutes and consume up to 2/3 of their body weight from the nectar of plants; they can service 20 flowers per minute. The wings of hummingbirds beat up to 55 beats per second and allow these tiny birds to fly at speeds up to 50 mph. They can hover and even fly backwards or upside down. 

Hummingbirds are primarily attracted to tubular flowers. They are stimulated by color, especially the color red. Clumps of bright red, orange and pink flowers are more visible to them than other colors. Plants with red, tubular shaped flowers are an excellent choice in the garden to attract hummingbirds. Other plants that attract these birds are gladiolus, honeysuckle, iris, lupine, nasturtium, petunia, and cosmos. 

Recently, I was asked if hummingbirds pollinate vegetables. I am having difficulty finding specific vegetables that they pollinate. That’s probably because there are not many vegetables with red, tubular shaped flowers, which attract the hummingbirds.  

Lastly, the Islands of Hawaii have no hummingbirds, but a one inch moth is often mistaken for this tiny pollinator. The hummingbird moth has grey beating wings with a quiet humming sound. Unlike like other moths, this fellow is diurnal and uses his long proboscis to ingest nectar from plants and flowers.  Hawaii's hummingbird moth is also a pollinator! 

Photo: University of Maine

Monday, June 29, 2020

The Plague of Powdery Mildew




Powdery mildew (PM) is a menace to many gardeners. The disease will turn large zucchini leaves white and later brown. A whitish cast will appear on many common garden plants such as tomatoes, beans, cucumbers, mustard, peas, and collards. Infected leaves often turn yellow to brown and may shrivel making the plant unproductive and eventually die.

The white fungal growth can develop both on the upper and the lower surfaces of the leaf, and sometimes, on flowers and fruit. The cottony like threads of this fungus travel along the surface of the leaf, occasionally sending “roots” down into the leaf tissue in order to obtain nutrients.

Many different types of powdery mildew fungi are host specific. This means that one particular mildew fungus will only infect those plants in a particular genus or family; the PM on the beans will not attack papaya, and the PM on mangoes will not attack tomatoes. 

The fungus likes temperatures between 60 and 80 degrees F being sensitive to temperatures above 90. Cool days and warm nights favor the disease. Spores of the pathogen are dispersed readily by wind. Even though this disease flourishes with high humidity, wet leaves can actually inhibit germination of the fungal spores, thus preventing infection. Because of this, the disease should be minimized during periods of heavy rainfall. Also during this time, the numerous spores that are on the leaves will be washed away.

Control Stopping powdery mildew in its earliest stages of development provides the best control. This can be done by sanitation: remove and destroy infected parts of the plant. Other measures of control are as follows: plant in the sunniest locations, provide good air circulation through pruning, and avoid excessive applications of fertilizer.

Fortunately there are a number of relatively safe and effective materials to use against this fungus - wettable sulfur, horticultural oils, including neem, and Kaligreen (potassium bicarbonate a relative of baking soda). Serenade is a biological fungicide, a bacterium, that helps prevent the powdery mildew from infecting the plant. Cucurbits (melon, squash, cucumbers) can be sensitive to sulfur.  Do not apply when the temperature is near or over 90 degrees and do not apply within 2 weeks of an oil spray. Use these materials in the earliest stages of disease development for best results.  Before spraying, it would help to remove the leaves that are heavily infested.  Do not dispose of them on the ground since they are loaded with fungal spores. Powdery mildews can attack healthy plants; but older plants, less vigorous plants and those that are stressed are more susceptible to infection.  



Most important, choose plant varieties (vegetables, fruit trees and ornamentals) which are tolerant or resistant to the powdery mildew fungus. For more information about seeds from locally developed vegetable varieties, contact the University of Hawai‘i at Manoa: http://www.ctahr.hawaii.edu/seed/seeds.asp. Or, contact your local university cooperative extension office. Note: Some of the resistant varieties will exhibit powdery mildew symptoms, but the disease is less severe. 

Photos: Cornell University, Colorado State University and USDA

Saturday, May 30, 2020

Plant a Rainbow of Colors in Your Garden


When planting a vegetable garden, let color be your guide to healthy eating.  For a number of years, scientists have been discovering the health benefits of the color pigments in food.  For some gardeners, a vegetable garden is lettuce, collard, mustard greens and kale- all healthy, leafy green vegetables.   But for health sake, add some color such as red tomatoes, yellow squash and purple eggplant.  Grow a rainbow of colors to the garden for good health.

Red colored fruits and vegetables contain natural plant pigments called lycopenes or anthocyanins. These compounds may help reduce the risk of several types of cancer, especially prostate cancer. By the way, the lycopenes in cooked tomatoes with a small amount of fat are absorbed better than lycopene from raw tomatoes.  Sun dried tomatoes are reported to have twelve times the lycopenes as raw ones. So plant plenty of tomatoes, beets, watermelon and red peppers. If there is room in the garden, include a pigmented citrus tree like pink grapefruit. 

Orange and yellow colors come from natural plant pigments called carotenoids.  Beta-carotene is converted to vitamin A which helps maintain healthy eyes.  Carotenoid-rich foods can reduce the risk of cancer, heart disease and improve the immune system function.  Plant plenty of yellow sweet potatoes, squash, pumpkins and carrots.  Citrus contains hesperidin, also found in the skin of tomatoes, and naringenin, which are anti-inflammatory and antioxidant. Curcumin, found in turmeric, known in Hawaiian as olena, has antioxidant properties. Turmeric is a popular Indian spice used in curries and other dishes.  Anecdotal evidence suggests that turmeric can be used to deter ants in the garden.

Other yellow and orange fruits grown in Hawai`i are pineapples, papayas and mangos. Pineapples contain bromelain, an enzyme which aids digestion.  Papaya and tangerines contain beta-cryptoxanthin, another carotenoid, playing an important role in vision and in bone growth. Papayas can easily be grown from seeds or purchased in abundance at local markets.

 Greens are colored by a natural plant pigment called chlorophyll.  Some greens contain lutein which helps keep eyes healthy. Here is a familiar list of green vegetables: green peppers, peas, parsley, watercress, arugula, spinach and kale.  Crucifers like broccoli and cabbage contain chemicals which may help protect against some types of cancer.  Leafy greens such as spinach and broccoli are excellent sources of folate, which is a B vitamin. 

The blue and purple colored fruits and vegetables also contain pigments called anthocyanins, powerful anti-oxidants which improve brain function and help to reduce the risk of cancer, stroke and heart disease.  Fig trees grow well in tropical and sub-tropical climates and should yield delicious, healthy fruit.  Anthocyanins, also found in strawberries and raspberries, act as powerful antioxidants that protect cells from damage. 

The whites contain pigments called anthoxanthins which are shades of white or yellow.   This group consists of onions, garlic, cauliflower, turnips, mushrooms, potatoes and bananas.  At least one of the group, garlic, contains a health-promoting chemical called allicin. This compound may help lower cholesterol and blood pressure and help reduce the risk of stomach cancer and heart disease. Potatoes, as well as bananas, are good sources of potassium.