CITRUS GROWERS ALERT

University of California researchers are telling citrus growers to check their groves for two new pests: (1) the citrus leaf miner, and (2) the citrus peel miner.

The citrus leaf miner (Phyllocnistis citrella) is an Asian pest that has been found in Florida since 1993. Within the last year or two, it was discovered in the Imperial and Mexicali Valleys on California’s southern border. The current world distribution of this insect suggests that it could survive and thrive on the Central Coast.

Damage: Larvae of citrus leaf miner form serpentine mines in leaves and fruit of citrus. Grapefruit, lemon and lime are most susceptible to damage, but the leaf miner attacks all varieties, as well as over 20 different plants belonging to the citrus family Rutaceae. Mines are characterized by a central line of frass, which can be used to separate them from mines of the native peel miner. The citrus leaf miner only infests young flushing foliage and lays its eggs on upper and lower surfaces of leaves less than half an inch in length. Pupation occurs in folds on the edges of leaves. Citrus leaf miner rarely attacks fruit.

Leaf miners have a short developmental time, and as many as six to 13 generations per year can be expected, depending on foliage flushing cycles and temperature. Infestation levels of one to three mines per leaf occur in Australia. In Florida, which has a much wetter climate, infestations of 15 to 20 miners per leaf are common.

Economic Impact: Economic losses due to the citrus leaf miner include: (1) Increased costs for protecting nursery trees and young non-bearing citrus, (2) reduced sales to home gardeners, and (3) increased orchard production costs, either directly through the use of pesticides (largely ineffective), or indirectly through treatments that disrupt biological control and integrated pest management programs. Except on limes, the loss of yield on mature trees because of foliage damage has not been demonstrated.

The citrus peel miner (Marmara sp. - new species) appears to be a native insect to the southwestern U.S. It was reported from Pasadena, California, in 1915. It normally attacks willow, however, oleander and citrus are also attacked. On citrus, the larvae almost always attack the fruit, rarely infesting leaves.

Damage: Larvae of peel miner form serpentine mines on the fruit of citrus. Grapefruit, lemon and lime are most susceptible to damage, but the peel miner attacks all varieties, as well as stems of oleander, avocado fruit, stems of cotton and leaves, and stems of willow. Under heavy infestations, peel miner will mine the leaves of citrus, but this is rare. Mines are serpentine and lack any associated frass line. Eggs are laid directly on fruit. Pupation occurs outside the mine in cracks or crevices in the tree within silken cocoons ornamented with small spheres. Peel miner has a short developmental time, and as many as six to 13 generations per year can occur.

Economic Impact: Citrus peel miner causes direct damage to the peel of grapefruit and although damage is cosmetic, as few as two to three mines per fruit can render fruit unacceptable for the fresh market. In 1995, a severe infestation in the Coachella Valley resulted in the loss of 80 percent to 90 percent of grapefruit in some groves. The peel of the fruit can become completely mined and take on an overall blistered appearance.

Currently, the citrus peel miner is found throughout Southern California as far north as Tulare County. For more information call our office 805/934-6240.

There are three types of skin cancer: Basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. The latter is the most dangerous form. The first two usually start as a small, firm nodule, or a small grayish red spot, or a red ulcerated, crusty patch of skin, or a crusty wart-like bump. Basal cells and squamosa cells are usually very slow-growing and take several months, or even years to develop. A malignant melanoma, on the other hand, may seem to appear over night. It may be black, brown, red, or shades in between. It may be slightly raised, or wart-like, and it usually has an irregular outline (not round like a mole).

Anyone who spends time outdoors, and especially anyone who has a fair complexion should see a skin doctor annually. For Central Coast residents, remember the fog is no protection. The ultraviolet rays that damage skin penetrate clouds and fog and do their damage even in cool weather.

The reason skin cancer incidence is less on the coast is that the cool climate forces us to wear clothes, which cover our skin and protect us. However, the back of the hands, the neck, ears, temples, and face are still exposed to the damaging rays of ultraviolet light.

Getting a sun tan provides no protection against skin cancer. In fact, regular sun tanning increases the risk of skin cancer. The tanning reaction of the skin is an attempt on the part of the body to protect itself against the damaging effects of solar radiation. Sun tanning and sunburns cause irreversible skin damage, which increases your risk of getting skin cancer.

To protect yourself, cover your skin. Wear long pants and long-sleeved shirts when you are working outdoors. Wear a broad-rimmed hat and cover exposed areas (back of the hands, neck, ears, and face) with sun block lotion, which has a rating of 25 or higher.

If you develop a patch of skin which itches, changes color, is sore, crusty, and resists healing, see your skin doctor. Also if you have a mole, which changes shape or color suddenly, or becomes itchy or sore, see your doctor.

Remember, malignant melanomas are a very deadly, fast-moving type of cancer. They should be attended to immediately on detection. Basal cells and squamosa cells are less aggressive, but also need to be removed promptly.

Finally, protect yourself when you are out-of-doors. Remember, there is no such thing as a healthy tan.

Idaho Studies on the use of trap crops for managing sugar beet cyst nematodes show promising results

The sugar beet cyst nematode (Heterodera schachtii) causes serious damage to cauliflower, Chinese cabbage, spinach, turnips, cabbage, and broccoli. The host range of this nematode is limited to crucifers, and under fallow or non-host crops, population levels gradually decline. In order to enhance these decline rates, trap crops can be used. Trap crops usually are closely related to the host plants of the nematodes and, like host crops, trigger the emergence of the juveniles from the eggs. The hatched juveniles usually do invade the roots of the trap crops, but once inside, are unable to establish a proper feeding site and die of starvation. The juveniles are unable to complete the life cycle, and no females or eggs are produced. Thus, trap crops offer the potential to "clean" the soil of the nematodes. The success of a trap crop depends largely on the ability of the crop to trigger hatching of the nematode juveniles from the eggs without allowing nematode reproduction.

Studies conducted at the University of Idaho, Parma Research and Experiment Station, showed that incorporation of trap crops, such as oil radish (Raphanus sativus spp. oleifera) or white mustard (Sinapis alba) in sugar beet rotation was the most economic and environmentally viable method for the management of sugar beet cyst nematodes. Cultivar selection within the trap crops is critical for its success, since the level of resistance to the nematode varies among the different varieties of oil radish and white mustard. Commercial varieties include oil radish "Adagio" and white mustard "Metex." A dense seeding rate is needed to suppress weeds and to maximize nematode egg hatching. Adequate soil moisture is important to ensure the establishment of the trap crop roots and resulting hatching of nematode eggs.

An eight- to ten-week growing period with soil temperatures above 60°F is critical for effective nematode control. New oil radish varieties that mature earlier, may shorten the necessary growing period. Seeding oil radish or white mustard in late summer, followed by chopping and incorporating in the fall, significantly increased yields and reduced nematode populations in sugar beet planted the next spring. Sugar beet yields increased 24.7 percent when following oil radish var. Adagio, and 21.5% following white mustard var. Metex compared to following a fallow period. Correspondingly, sugar beet cyst populations declined by 92 and 84 percent under oil radish and white mustard, respectively, but only by 41 percent under fallow. Following trap crops with a non-host such as potato, lettuce, onion, celery or beans will further improve nematode control.

These studies from Idaho clearly demonstrate the potential of trap crops for managing sugar beet cyst nematodes and may also be useful under California growing conditions.

For further information or questions, please contact Franklin Laemmlen, 805/934-6240.