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کشاورز ایرانی (مرکز ارائه خدمات جامع آموزش کشاورزی)

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یکشنبه 15 فروردین 1389

WHAT IS BLOSSOM END ROT ON TOMATOES

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 


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Blossom end rot is perhaps the most common physiological disorder you will experience with growing tomatoes. Typically it shows itself as a circular, dark brown patch of skin found at the flowering end of the fruit – hence the name. As the fruit grows this unsightly dark patch gradually toughens and shrinks back into the fruit.

What Causes Blossom End Rot?

This disorder is caused by a deficiency of calcium within the plant and its relatively poor mobility through the plant tissues. This is important as calcium is not only a valuable component within the plant cell walls and is also vital in the production of new cell walls and the normal function of plant membranes. Because of this, the problem of calcium deficiency is most noticeable in areas where there is significant cell division, and when you consider the rapid growth generated in the production of a tomato fruit it is understandable why cell death (necrosis) can occur in this region when the availability of calcium is restricted.

Calcium deficiency should not be confused with lack of availability as its uptake can be inhibited by high levels of potassium, magnesium and /or ammonium-nitrogen within the root environment. Surprisingly other factors that can inhibit the uptake of calcium can include water stress and high humidity. To a lesser extent boron deficiency can also be a factor as it is needed for the transport of calcium within the plants tissues.

How to Treat Blossom End Rot

There is no magic bullet to deal with blossom end rot and this is because of the complex inter-relationships that calcium has with other elements within the plants cells. However a holistic approach is normally best although signs of improvement are usually slow to appear.

It's probably worth doing a pH test first as acidic soils have naturally lower levels of calcium compared to alkaline soils. If this is the case then apply lime to the soil, but go by the manufacturer’s recommendations according to soil type - try to end up with a soil pH of about 6.5. You can also consider spraying the affected fruit with solutions of calcium nitrate or calcium chloride. This is applied at a concentration of 2 grams per litre on a fortnightly basis.

In the greenhouse environment it's important to keep humidity levels low, so make sure there is good ventilation throughout the growing space. Air circulation can be further improved by removing the older, lower leaves from the base of the plants.

Never apply fertilizer to dry soil and any irrigation that is in place must be sufficient to maintain a good, steady, growth rate for the plants – this is particularly important during the summer period. For outdoor tomatoes, giving the soil a good mulch can be very helpful in maintaining water levels in the soil especially in times of moisture stress. When feeding your plants use either a specific tomato fertilizer or use fertilizers that are low in nitrogen, but high in superphosphate.

Although all of these solutions will help in some way to reduce the incidence of Blossom End Rot in tomato plants it is always best to try and avoid the conditions that promote it in the first place. By using good plant husbandry as outlined above you will hopefully never have a incidence to worry about controlling.

یکشنبه 15 فروردین 1389

SMALL FRUITS

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 

SMALL FRUITS


Raspberry Crown Borer


Damage from larval feeding is now showing up on infested raspberries, even though larvae have been active in cane roots and crowns all summer.  Canes will have wilted, dried leaves from top to bottom.  Pull on the cane and it should come out of the soil fairly easily.  You will be able to see boring damage (shown at right), and galleries.

Pull out as many infested canes/plants as possible, and look for larvae.  The more larvae you remove, the more you will have reduced the population.  In late summer and early fall, larvae will leave the crowns and move to the roots for the winter.  This period of the season is recommended as the optimal timing for control (which is a root drench of bifenthrin).  More information on control options and life cycle in a later issue.

یکشنبه 15 فروردین 1389

Powdery Mildew

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 

Powdery Mildew

Powdery mildew is showing up on many vine crops, especially where plants are running together, or in low spots. This disease first appears as small circular, white lesions located randomly on the leaf surface or on petioles. As the infection continues, leaves turn yellow and become distorted. Fruit are usually not directly affected, but yield and flavor can be reduced. This disease thrives in humid and shady environments under moderate temperatures (up to 80 degrees F). Free water is not necessary and can actually inhibit germination, as can very hot temperatures. 

Scout for the disease by looking on mature leaves in the middle of the field or garden for the white, powdery lesions. In general, if you find one lesion per 50 older leaves, begin a regular, weekly protectant fungicide program.

Treatment:  potassium bicarbonate (Kaligreen, Armicarb), horticultural oil (JMS Stylet Oil), sulfur (Safer Garden Fungicide), Bacillus subtilis (Serenade)

NOTE: to prevent plant damage, do not use oil or sulfur within two weeks of each other, and do not spray when temperatures are over 90 F.

یکشنبه 15 فروردین 1389

Tarnished Plant Bug (lygus bug)

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 

Tarnished Plant Bug (lygus bug)
A quiet moment shared between two “enemies of man”: grasshopper and lygus bug

Tarnished plant bugs have been spotted on several vegetables and herbs in northern Utah.  As nearby alfalfa fields are cut, or weeds dry, these plant bugs move to alternative food sources.  They mostly feed on flowers and fruit, but sometimes move to foliage.

They feed with sucking mouthparts and their saliva is toxic to plants, killing the tissue at which it feeds.  Examples of some damage:

  • broccoli: dry, shriveled flower buds scattered across the head
  • lettuce/cabbage: necrotic lesions along midrib that causes distorted leaves 
  • eggplant/pepper: feeding is limited to flowers, killing them
  • tomato: feeding on fruit causes similar damage to stink bug injury; feeding on green fruit causes cat-facing (severe dimpling and distortion)
  • potato: usually feed on leaves and flowers only, resulting in wilting, distorted, yellow leaflets and aborted flowers

Adults are very mobile and can move in and out of fields and between gardens rapidly, making monitoring and control difficult.  As such, no chemical will give 100% control in vegetable gardens or fields.  To suppress populations, remove overwintering sites such as thick weeds along field edges, and debris/brush piles.

ادامه مطلب

یکشنبه 15 فروردین 1389

Wilting caused by Squash Bug

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 

Wilting caused by Squash Bug



Squash bugs have been active for several weeks on squashes, pumpkin, and melons. In areas of heavy feeding, wilting and death of leaves or plants is occurring. This is sometimes referred to as “sudden wilt.” Adult squash bugs can feed on the vines and stems, puncturing through the xylem cells, and preventing water transport up to the leaves.  Eventually, leaves become dry and turn black. Sudden wilting can occur on individual leaves, a section of a plant, or an entire plant.

In the eastern US, squash bugs can introduce a bacteria that also causes wilt, but bacterial wilt is not known to occur in Utah.

Treatment:

commercial: acetamiprid (Assail), esfenvalerate (Asana), permethrin (Ambush, Pounce), bifenthrin (Tundra), carbaryl, lambda-cyhalothrin (Warrior), piperonyl butoxide+pyrethrin (Pyrenone)

residential: neem oil (Concern, Ferti-Lome), permethrin (Ace Dust, Bayer Advanced Dust, Bonide Eight), kaolin clay (Surround), carbaryl.

NOTE: carbaryl can cause phytotoxicity (plant damage) when applied in hot weather.

یکشنبه 15 فروردین 1389

Blossom-end Rot

نویسنده: مهندس علیرضا شعاعی   طبقه بندی: بیماریهای گیاهی، سایر، 

Blossom-end Rot

Blossom-end rot can show up at any stage of a tomato but is most commonly seen near harvest.  Initially, a small water-soaked lesion will show up at the blossom end of the fruit, and will enlarge and darken as the fruit develops.  The lesion eventually becomes flattened, black, and leathery.

Blossom-end rot is an abiotic disease associated with a decrease in water and low concentration of calcium in the fruit.  Calcium is required for normal cell growth, and if a plant is growing rapidly due to optimal conditions and then suddenly deprived of water, the demand for calcium exceeds the supply, so the tissues of the fruit at the blossom end break down.  Calcium availability can also be affected by excessive soil moisture fluctuations, rapid vegetative growth due to excessive nitrogen fertilization, high soil salinity, or destruction of roots by cultivating the soil too close to the root zone.

Treatment: If you suspect blossom-end rot, be diligent about maintaining adequate and even soil moisture, and mulch soil if necessary.  Be careful when cultivating soil, and use a fertilizer low in nitrogen and high in phosphorus (4-12-4 or 5-20-5) to alleviate the problem; foliage can also be sprayed with a calcium chloride solution, until a balanced soil moisture is established.  Note that calcium chloride can be phytotoxic if applied too frequently or in excessive amounts.

چهارشنبه 19 اسفند 1388

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