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Q. I purchased a potted kumquat last spring, and during the fall and winter it developed yellow blotches on its leaves. Now it is February and there is a lot of new growth on the branches. The new growth hasn't developed the yellow blotches. Any idea what is causing this yellowing, and should I be doing something about it?
- D. L., Helena, MT
A. Yellow leaves can be caused by many things including lack of nitrogen, insufficient light, water-logged soil (plant roots need oxygen to thrive), dry soil, or iron deficiency. If the older bottom leaves are yellow, but new growth is green, the plant may be suffering from a lack of nitrogen, or may have dried out at some point. If new leaves are yellow with green veins, the problem may be a lack of iron. (Lack of nitrogen is a more common problem than lack of iron.) Soil should be kept moderately moist (but not wet). The yellowing could also be the result of transplant shock or being moved from an ideal greenhouse or nursery environment into your home. Since the new growth is healthy and green, the latter is the likely explanation. Just keep up a regimen of good cultural practices (appropriate water, sunlight, fertilizer) and your kumquat should be fine.
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Q. Last year the raspberries on one end of the patch were small, and crumbly, although the foliage appeared to be normal. The other end of the patch receives the same light, soil, and water, and these berries were large and juicy like normal. Should I destroy the canes with small berries? What could it be, and is it contagious?
- L. R., Mercer, ND
A. "It sounds like your patch is suffering from the aptly named crumbly berry virus, or perhaps another similar virus. Raspberries are especially prone to viral diseases, which is why it is very important to purchase certified virus-free stock when planting a new patch.
Crumbly berry disease is is caused by the tomato ring spot virus and spread by the dagger nematode. Plants may appear normal, but will produce small fruit that fall apart when picked. This is a result of the failure of some of the drupelets in the berry to develop. This virus has a wide host range including many weeds such as dandelion.
Unlike some viruses, the organism can live for years in dead plant material, so when you remove the infected canes, get as much of the roots, crown, and canes as you can and burn or bury them. The virus is spread by aphids, so if you noticed these pests on your healthy canes last year, be aware that they may have infected more of your patch. As a safeguard, you can order new, disease-free stock this year and plant it at least 200 yards from your current patch, if you have the room, so you won't have a break in harvest if your current patch is affected this year."
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Q. The leaves on my peach tree are getting pink raised blistery-looking patches on them. Do you know what it is, and how can we fix it?
- L. M., Canal Winchester, OH
A. "It sounds like your peaches are suffering from a fungal disease called peach leaf curl. It can affect leaves, flowers, tender shoots and even fruit. Those diseased leaves will fall off soon, but unaffected leaves will grow normally. Infection occurs in spring when temperatures are around 68F degrees and surface moisture is present on the leaf buds. Therefore the problem doesn't occur every year with the same severity. Once you see the symptoms on the leaves it is too late to correct it for this season.
Sanitary measures can help control the disease, so it's a good idea to collect and discard fallen, affected leaves, and to prune twigs with the small, seldom-noticed swellings caused by the infection.
A minor infection won't harm the tree, but repeated or prolonged infection can weaken the tree. The lowest toxicity option for effective control is to apply a copper fungicide at the beginning of dormancy in the fall. Copper will cause the peach to defoliate so that is why we wait until the leaves begin to fall to apply it. Note that copper can stain masonry blue, so be careful in applying the spray if your tree is near a sidewalk, rock wall of your home, etc."
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Q. My ever bearing strawberries are rotting and the fruit is covered with a gray mold. Is it due to the extremely high amount of rain this year, and is there anything I can do?
- N. D., Stratham, NH
A. "You've pegged it -- gray mold (Botrytis) rears its ugly head in cool, humid conditions (including places like your refrigerator). The spores are everywhere, but they only attack damaged or dead tissues, such as those of your bruised and soggy berries. If you can somehow prop up the berry branches to keep them off the ground, not touching each other, and where the breeze can keep them relatively dry, you'll have better luck. Many growers use a thick layer of straw mulch to keep the berries from touching the ground. Remove infected, bruised or otherwise damaged berries to further deter it from spreading.
It may be too wet to try this now, but you can take steps to keep this from happening in the future by dosing your plants with compost tea. Beneficial organisms in compost fight off fungal spores and the nutrients boost plant health. Here's how scientists brew it when conducting experiments:
1. Mix one part mature compost that includes some rotted manure (horse, cow or chicken) with five parts water. (Make sure that the material is fully composted, so potential pathogens associated with manures will be killed.)
2. Allow the mixture to sit and ferment in the shade for 10 to 14 days.
3. Filter the mixture through cheesecloth to remove chunks. The stuff can smell pretty bad, so don't do this in your kitchen!
4. If you must dilute it to stretch the batch, don't dilute by more than half.
5. Spray or coat upper and lower plant surfaces. Repeat every 2-3 weeks."
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Q. "I have a mature concord grape vine that has been pruned regularly. This spring the new branches are breaking off from the main branches in large numbers. Also some of the new growth appears wilted on the ends of some branches. I have examined the broken branches but do not see any insect damage. What could be causing this?"
- M. C., Lynchburg, OH
A. "These symptoms are typical of the work of a weevil called the grape cane girdler. Check inside the fallen shoots for tiny white legless larvae. If they are present, you have cane girdlers on your hands. Pick up all of the fallen shoots, and cut off damaged shoots that are still clinging to the vine, as they contain larvae or pupae of the pest. Squash, burn, or bury the shoots to kill the pests. Generally the damage is minimal and doesn't affect your crop because the pests tend to infest shoots beyond the grape clusters. Keep tall weeds cut from the area surrounding the vine. Inspect other shoots for evidence of the pest, and cut these from the vine. These precautions will keep the number of pests well within the tolerance of a vigorous grape vine."
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Q. "My peaches and plums rot before they are fully ripe. What is causing this and how can I stop it?"
- J. F., Georgetown, DE
A. Brown rot, caused by the fungus Monilinia fructicola, is a common disease of peaches and plums; it also attacks nectarines, and cherries. The disease may affect blossoms, twigs, and fruit. Generally, there are two major infection periods of the brown rot fungus. They occur during blossom and beginning several weeks before harvest.
The blossom blight phase occurs in early spring during bloom. Young petals first develop brown spots, but the blossoms quickly turn brown or black and die. Small tufts of dusty brown to gray fungal growth can be seen growing on the dead blossoms. The loss of some blossoms in the spring is not serious in itself; however, inoculum produced on the rotting blossoms serves to infect developing fruit later in the season. The fungus also may move from blighted blossoms into the twigs, causing small, elliptical cankers. In some cases, these cankers will girdle and kill twigs. Sap bleeding or gum production often is associated with twig cankers.
The second phase of the disease occurs as fruit begins to mature. Inoculum produced on blighted blossoms, twig cankers, or from nearby wild plums infects maturing fruit. Affected fruit develops light brown spots that enlarge rapidly. The fruit may be completely rotted within a day or two. The fungus sporulates profusely on the rotting fruit, giving the peaches a dusty brown appearance. The rotting fruit shrivels to form a structure called a mummy, which is completely colonized by the brown rot fungus. These mummies may remain attached to the tree or drop to the ground. Here are some ways to control brown rot:
Clean up fallen leaves and fruit at the end of the season, and remove and destroy any mummified fruit that remains on the tree. Plant trees in full sun; space trees generously and prune annually to maximize air circulation. Thin fruit so they aren't touching. Inspect branches and prune off affected wood. Spray sulfur during bloom and again before harvest if weather is wet and humid. Although no varieties are completely resistant, two varieties, 'Newhaven' and 'Harrow Diamond,' have been shown to have some resistance to the brown rot fungus.
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Q. "A week ago I planted two Monterey Bay Bush Cherry topiaries in pots along a walkway. I uses fresh potting soil recommended by my nursery and I treated the root ball and soil with a vitamin B1 product following label instructions to help prevent shock. I mulched them with a 2-inch layer of redwood mulch for moisture retention, and water daily until I can see water begin to build up on top of the mulch. However, I've noticed that many of the leaves (especially on the tips) are turning brown and drying out. It has been very warm, with temperatures in the high 80s. What is wrong with my plants? "
- B. B., San Jose, CA
A. "You have worked hard to make sure your shrubs get a good start, but it sounds like you are overwatering them. It's true that soil around newly planted shrubs should not be allowed to dry out, but too much water can be detrimental to the shrub's ability to develop roots it needs to stabilize and start new growth. Containers are tricky, too -- if they don't have ample drainage, the plants may feel like they're sitting in a bowl of porridge. The high temperatures may well be exacerbating the symptoms.
Base your watering practice on how the soil feels. One good test of soil moisture is to stick a pencil or Popsicle stick into the soil to a depth of a few inches. Pull the stick out at an angle. If soil adheres to the stick, it is moist and you can skip watering that day. The mulch you have applied will go a long way toward maintaining even soil moisture."
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Q. The tips of many of my strawberries this year are hard and very seedy. What causes this, and how can I prevent it?
A. It sounds like the damage is caused by the tarnished plant bug (TPB). The wingless yellow or tan nymphs are 1/8 inch long and somewhat resemble aphids; adults are about 1/4-inch long and 1/8-inch wide, flattened and oval in shape; wings are folded flat over the body. Both the nymphs and adult insects feed by piercing the plant and sucking out sap, at the same time injecting a toxin into the plant tissue.
On strawberries, the insects usually feed on a cluster of seeds on one area of the berry; these seeds abort and stop producing growth hormones, so the tissues surrounding the area ceases to grow. Severe deformation is commonly referred to as "buttoning" or "catfacing" -- the hard, seedy tips you describe.
Tarnished plant bugs are found throughout the country and attack a variety of vegetable, fruit, forage, and flower crops, as well as a number of weeds. Among fruits, it attacks not only strawberries but also apple, peach, pear, and most other deciduous and small fruits.
TPB is difficult to control because the insects have many different plant hosts and many generations a year. Good garden sanitation is the first line of defense. Keep weeds controlled in the strawberry beds and around the garden where tarnished plant bugs may be hiding. Most of the damage to spring-bearing strawberries is done between petal fall and young berry formation. However, for best control, reduce the population of tarnished plant bugs before petal fall. Begin checking the flower buds and foliage for nymphs weekly, starting when flower buds are first evident. If you spot nymphs, spray with insecticidal soap, being sure to cover the undersides of the leaves completely.
Attracting beneficial insects to your garden may help in controlling the pest.
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