Diseases and Pests of Fruit

November 19, 2012

 A pest is any organism that negatively directly or indirectly affects fruit quality either pre- or post-harvest. Pests that attack fruit crops include bacteria, mollicutes: (Bacteria without cell wall, phytoplasmas), fungi, insects, weeds, and nematodes.

Then we have bacterial diseases that can cause damage to fruit, leaves, and stems. They spread by tools, wind, rain, and labor. They can be control with genetic resistance, chemical sprays, which may not be very effective, and sanitation. 

Bacterial Diseases and the Fruits they affect:

•  Fireblight – apples, pears
•   Citrus canker, greening -oranges, grapefruit 
•  Bacterial canker – peaches
• Bacterial Leaf Spot
•  Crown gall - apples, peaches, cherry, grapes

Fungal Diseases can affect leaves, fruit, stems, and roots. They spread by soil and aerial means (rain). They can be control with genetic resistance, fungicides, and biological ways (natural).

 

Important Fungal Diseases and the Fruits they affect:

•  Black sigatoka – banana 
•  Fusarium, many crops – bananas
• Brown rot – peaches, citrus
• Black rot/ripe rot (postharvest) – grapes
• Scab – apple, citrus, peach
• Powdery mildew (dry environment) – grapes, apples, chestnut, cherries
• Wilt – grapes, blackberries, raspberries
• Anthracnose – avocado, mango

Mollicutes are similar to bacteria, lack cell walls, and survive on inorganic sources. They have a life-like similar to bacteria, and decline symptoms similar to viruses.

Important Mollicute Diseases and the Fruits they affect:

• Witches Broom – Limes
•  Stubborn Disease (spiroplasma) – Oranges
• Pear decline
•  Lethal Yellows (phytoplasma) – Coconut
•  Grapevine Yellows

Virus Diseases are the most severe of all diseases. They spread by budwood, budding, grafting, insects, mites, nematodes, and pollen. They can be control with genetic resistance and heat therapy.

Important Virus Diseases and the Fruits they affect:

• Citrus Tristeza: (mites)
•  Apple Mosaic – apples, peaches (pollen)
•  Papaya ring spot spread (Aphid)
• Tomato ring spot - apple, stone fruits (Nematode)

Other Common Pests of Fruit Crops

•  Insects
•  Mites
•  Animals – deer, moles/voles
•  Snails

Pruning and Fumigation

November 14, 2012 

Pruning is the removal of a portion of a tree to correct or maintain tree structure. Training is a relatively new practice in which tree growth is directed into a desired shape and form. Training young fruit trees is essential for proper tree development. It is better to direct tree growth with training than to correct it with pruning.

As a principle of pruning, use sharp tools to make sharp cuts to avoid extended pieces of branch (nubs). It is not recommended to cut close to trunk instead make collar cut to avoid cracking the branch of the tree and there is no need to paint cuts.

Pruning is most often done during the winter, commonly referred to as dormant pruning. Training includes summer training and summer pruning as well as dormant pruning. The goal of tree training is to direct tree growth and minimize cutting.

BENEFITS OF PRUNING:

Balance cropload and vegetative growth.

Improve light penetration.

Improve insecticide/fungicide efficacy.

Increase air movement.

Decrease disease.

Increase fruit size (Thin fruit buds, reduce yield)

Facilitate mechanical harvesting.

Rejuvenation.

Fumigation 

Fumigation is use to eliminate nematodes, replant disease and eliminate or reduce weed populations, which are all serious factors that inhibit the proper development of fruits crops.

Acute fumigant poisoning causes eye irritation, sore throat, headaches, nausea, vomiting, breathing difficulties and aggravated asthma, and neurological effects such as convulsions, dizziness, or tremors. Fumigant exposure also has long-lasting effects that include cancer, respiratory damage: Exposure to fumigants can cause permanent respiratory damage, neurological effects, reproductive & developmental effects, immune system effects, and endocrine disruption.

Soils for Fruit Crops

November 7, 2012

We learned about soil characteristics because people need to know the proper aspects of soils for them to grow their fruit crops. Some of those factors are pH of soil. pH can affect nutrient solubility. If pH is too high, it limits the macronutrients needed by the plants. Cation Exchange Capacity is the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given pH value, available for exchange with the soil solution. CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination.

Fertilizer Tests help to determine nutrient levels

Soil tests are the analysis of a soil sample to determine nutrient and contaminant content, composition and other characteristics, such as acidity or pH level. Tests are usually performed to measure the expected growth potential of a soil. They play a great role before growing a certain fruit crop.

We also talked about plant tests. Soil and herbage analyses help pastoral farmers and their advisers choose the best fertilizer programmed. They also highlight mineral imbalances that might be affecting the health of pasture or animals that feed on it.

Herbage tests of pasture complement soil tests and allow important trace nutrients like cobalt, selenium, copper and iodine to be adjusted for improved animal health. Using both herbage and soil testing will provide a better overall picture of the farm nutrient status for an improved fertilizer programmed.

Moreover, Fertilization Methods were addressed in class. They can be broadcast, which is when application is over entire orchard floor. Banding, it is applied within tree root zone. And fertigation is applied through irrigation system and delivered in small doses.

Fruit Quality and Dormancy

October 29 – November 2, 2012

We learned that the factors in fruit quality are size, shape, color, blemishes, and texture. Fruit Skin Blemishes are a problem because they affect marketability of fresh fruit. People’s perception towards fruit skin blemishes lead to a decrease of sales of the fruits affected by them. They biotic causes of fruit blemishes are insects, mites, bacteria, and fungi. Then we covered in class the abiotic causes were wind, hail, sunburn, and low or high temperatures.

Further, the fruit maturity factors. Fruits can be climacteric and Non-climacteric. Climacteric fruits refer to fruits that have high respiration rate during the fruit's ripening. During the ripening process of climacteric fruits, the production of a phytohormone, ethylene, dramatically increase up to 1000-fold of the basal ethylene level. Climacteric fruits are ones that are able to ripen after being picked. Examples of climacteric fruits are bananas, apples, pears, and avocados. On the other hand, Non-climacteric fruits are fruits that does not ripen after harvest. Examples of non-climacteric fruits are citrus, grapes, cherries, raspberries, strawberries and cashews.

Dormancy is a state of temporary metabolic inactivity or minimal activity. Plants generally go dormant in response to adverse growing conditions. For example: perennial plants going dormant for the winter or grass going dormant in intense heat. They stop growing and conserve energy until better cultural conditions present themselves. This happens naturally as seasons and weather changes. It can also be artificially controlled to store plants for shipping or to get them to flower for particular holidays. Forcing bulbs and flowering branches in the spring is a way of artificially breaking dormancy.

Examples:

It's helpful to mulch over perennial plants, once the ground has frozen, to prevent them from breaking dormancy too soon.