Garden Talk

with Rebecca Jordi


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Q: How do I control whiteflies on my leafy green vegetables?

 

Whiteflies

Whiteflies

 A:  Whiteflies feed exclusively on leaves, nearly always occurring on the undersurface. They suck juices from the plants and also excrete large quantities of honeydew in which sooty mold grows. Leaves will be sticky if there are many whiteflies feeding on the leaves above them and may turn black with sooty mold which grows on the honeydew. The most common whitefly found on Florida vegetables is called the silverleaf whitefly (http://edis.ifas.ufl.edu/in286) because of the effect its feeding has on squash leaves. Feeding by the immature stages or nymphs can also result in white areas in tomato fruits, streaking of pepper fruits, and blanching of broccoli stems. Whiteflies are not flies but are distant relatives of aphids and leafhoppers and, like them, feed on plant sap with piercing- sucking mouthparts. Whiteflies can spread some plant viruses, such as tomato yellow leaf curl virus and bean golden mosaic virus. The adult is a very small (less than 1/16 inch long) and has white wings dusted with a waxy substance. It holds its wings like a tent over its yellow body (Figure 26). It lays its eggs on the lower surface of leaves of many plants, including tomatoes, eggplant, melons, cucumbers, squash, okra, beans, cabbage, and broccoli. Except for a very brief time after hatching, the nymphs cannot move on the plant and look like clear or pale yellow scales. Regular applications of insecticidal soap may help keep whiteflies under control. Tiny wasps also attack the whiteflies. Flowers planted around and in the garden may help these wasps and other beneficial insects survive by providing a source of nectar. Other general purpose garden insecticides that kill on contact may also be helpful but will harm the beneficial insects. Because the insects are found on the lower leaf surface, sprays must be directed there in order to be effective.

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Q: What is the name of the insect and what does it do? It looks like it has a long stinger at the end of the abdomen.

Broadnecked Root Borer

Broadnecked Root Borer

A: I believe the insect you brought in to the office is a Broad-neck root borer, possibly Prionus laticollis.  The female is much larger than the male, growing to two inches or more. The structure you see at the end of the abdomen is actually called an ovipositor, not a stinger. Ovipositors are structures on female insects in which they deposit eggs. This particular insect deposits eggs into the ground around trees and shrubs. The yellow eggs are about 1/8 inch long developing into larvae which then feed on the living roots of trees and shrubs. One female may lay as many as 100 eggs in clusters. The larvae may be as long as 3 ½ inches with black mandibles (very scary).  Broad-neck root borers prefer deciduous trees of the forest but have been known to feed on fruit trees and shrubs such as peach, pear, apple, blueberries and even grapes. The complete life cycle takes about three years. Adults emerge from the ground between June and August eating the foliage of trees and, on some occasions, even damaging the fruit.  Generally, the adults feed at night but stay hidden during the day. The smaller males are seen more often as they are attracted to light. Broad-necked root borer’s range is from Quebec and Ontario to Minnesota and as far south as Florida.  Because the larva of this insect feeds exclusively on the roots of trees, the only visible symptoms are limb die-back and the yellowing and/or thinning of foliage. Borers can completely destroy young trees and make older trees more susceptible to being blown over.  Prevention is the best way to deal with a borer. Keep grass, leaves, mulch, bark and other litter cleared away from the bases of trees. This prevents the borer from having a place to hide and makes it more visible to predatory birds. In addition, avoid over pruning, over fertilizing and over watering trees – all of these can cause additional stresses. 


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Q: I am having a terrible time with the squirrels eating the bark from my maple and oak trees. What can I do?

Squirrel

Squirrel

A:  Eastern Gray Squirrels are the most frequently seen mammal in our area. They are members of the Rodent family, and spend most of their lives in trees. Eastern Gray Squirrels usually live to be about five years old. They survive with their good sense of vision, smell, and hearing. Although squirrels may be amusing to watch (except when they are eating my bird seed); they can indeed damage trees significantly.  They typically strip bark during winter and spring but there is no reason to think this could not occur any other time of year. Deciduous trees with smooth bark sustain the most damage, but other trees can be targeted.  Remember, deciduous trees are the ones dropping their leaves in the fall. Twig clipping occurs most frequently in spring and early fall. Fortunately, trees can sustain damage up to 50 percent of the trunk’s circumference and foliage losses up to 30 percent without significant impacts. If the squirrels chew more than 50% of a limb it is possible for the limb to die and ultimately break off and fall to the ground. Landowners can prevent damage to trees by installing metal collars. The metal collars can be used to encircle trees and prevent squirrels from traveling up and down the limb. Collars should be at least 2 feet wide and placed 6 to 8 feet above the ground. Collar edges should be overlapped and connected by springs to allow for tree growth. These same types of collars could be placed on the limbs.


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Q: Rabbits are eating my Asiatic jasmine. What can I do?

Marsh Rabbit

Marsh Rabbit

A:  As youngsters, we have learned to love these furry little critters but now as landowners we have a very different perspective.  I have a few hints which should help:  1. Removing dense, heavy vegetative cover, brush piles, weed patches, junk dumps and stone piles adjacent to the landscape will help eliminate rabbit habitats.  2. Fencing made from chicken wire, with mesh less than 1″, can be placed around a vegetable garden or herbaceous plant border. The fence must be at least 2′ high with the bottom buried at least 3″ deep.  3. You can also use cylinders of 1/4″ wire hardware cloth extending higher than a rabbit’s reach by placing them around the trunks of individual trees and shrubs. Bury the bottom of the cylinders 2″ to 3″ inches below ground level and place them 1″ to 2″inches from the trunk. 4.  There are a few plants rabbits don’t particularly like: yarrow, aster, wild indigo, daylily, geranium, iris and sedum.  5.  There are plenty of things on the market which supposedly repel deer and rabbits such as products containing capsaicin, which is the main ingredient in hot chili peppers.  But we have no extensive research to support their claims.


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Q: What is causing the new leaves on my ficus plants to fold in half? I have been told they are thrips.

Weeping fig thrips

Weeping fig thrips

A:  After talking to you about bringing a sample in a sealed plastic bag to the office, I was able to determine they were most likely Weeping fig thrips, Gynaikohrps uzeli.  Since the plants at your nursery were originally brought in from South Florida, it was important for me to notify the Florida Division of Plant Industry plant inspector about spotting this insect pest.  We do not want these insects to become established here as it is quite possible for the insects to feed on other landscape plants which could lead to some serious issues.  Weeping fig thrips is a very large thrips compared to the flower and chili thrips we are more accustom to seeing in this area.  They are dark black and can be plainly seen without the aid of a stereoscope or eyepiece whereas flower or chili thrips are best seen using magnification aids. Weeping fig thrips typically feed on the new leaves and cause them to fold onto themselves, covering the thrips. The feeding causes blotches on the leaves and can lead to pre-mature leaf drop. Chemical control is difficult but professionals have chemicals available with the appropriate pesticide license.  Such products as Merit and Safari can be used as a soil drench (poured around the root area of the plant). This will allow the chemical to be absorbed through the roots and then the chemical will move to other parts of the plant eventually reaching every leaf.  When the insects feed on the leaves they will take in the chemical and you should see some control in your nursery setting.