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Thrips, Western Flower Thrips / Order Thysanoptera

                     (Frankliniella Occidentalis)

                     Adult thrips are small and slender, (less than 1/20 inch long), and have long fringed or hairy wings on the margins. Immature thrips (larvae or nymphs) are similarly shaped with a long, narrow abdomen but lack wings. Most thrips range in color from translucent white or yellowish to dark brown or blackish, depending on the species and life stage. A few species are more brightly colored.        

Damage:        Thrip feeding on plant leaves may result in leaf scarring, necrotic spotting and distorted growth. In addition, adults feeding on flowers or unopened buds may lead to flower bud abortion or deformed flowers.

Solutions:     Healthy plants can usually tolerate Thrip damage; however, high infestations on Marigolds may justify control. If control is necessary, use an integrated pest management control (IPM) strategy that combines the use of good cultural practices together with conservation of natural enemies using specialized low toxic chemicals such as narrow-range oils and Bio-Insecticides. 


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Leaf miner / Order Diptera

                       (Liriomyza spp.)

                     Leaf miners are an important pest of Marigolds worldwide. Adults are small, 0.07-0.13 inches. long, shiny, black flies with yellow markings on their abdomen. Liriomyza trifoliiis is one of the most common leafminers found on ornamental crops and Liriomyza huidolorensis, the pea leaf miner, is also a serious problem of ornamental crops.

Damage:      An adult female leafminer causes damage by puncturing leaves with her ovipositor whilst laying eggs. This creates white specks on leaf surfaces. Eggs hatch into bright yellow to white larvae that feed on the mesophyll layer of cells creating mines within the leaf. This damage reduces photosynthesis and may eventually kill plants.


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Common Cutworm / Order Lepidoptera   

                        (Spodoptera litura fabricius)

Damages :      Most common cutworms damage the leaf and the flower of Marigolds. Common cutworms are active throughout the summer. They are rarely a problem during spring. Cutworm populations can vary greatly from year to year and when abundant can devastate a Marigold crop. Most of the damage caused by common cutworms occurs when they chew stems of young plants slightly above or below the soil line. Some cutwords, e.g. black, bronzed, and army cutworms, can have a devastating effect on Marigolds, attacking and cutting/chewing new plants nightly.


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Cause :         Fungal Wilt cause by Fusarium sp.

Symptoms :  The first symptoms are yellowing of the foliage, beginning with the lower leaves and working upward. Yellowing often begins on one side of the plant. Infected leaves later show downward curling, followed by browning and drying. The top of the plant wilts during the day and recovers at night, but wilting becomes progressively worse untill the entire plant is permanently wilted. Vascular browning can be seen in infected stems and large leaf petioles. Affected plants' root systems are stunted. The degree of stunting depends upon time of root infection. Plants infected when they are young will be more severely stunted than plants infected at a later stage. 

Solutions :    The disease is difficult since the pathogens are commonly found in soil. One of the key strategies for control of vascular wilts is prevention. Therefore, it is important to avoid planting Marigolds in infected soil. It is also helpful to maximize plant vigor by good cultural care and watering. Careful handling of plants will avoid root injury which enables the fungus to enter the plant. Since repeated use of the same area greatly increases the amount of disease, rotation is essential. When available, it is also helpful to use resistant varieties. 


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Bacterial wilt, Ralstonia sp. 

Symptoms :  Above-ground symptoms include wilting of 1-2 leaves on young plants during the heat of the day. Such plants tend to recover at night. On large-leafed plants, only the tissue on one side of the mid-vein may wilt. This is very common for plants; such as, Nicotiana. Affected leaves turn yellow and remain wilted after time. The area between leaf veins dies and turns brown. Usually the main stem of the affected plants remain upright, even though all the leaves may wilt and die. Internal symptoms include light tan to yellow-brown discoloration of the vascular tissue. Long sections of infected stems reveal dark brown to black streaking in the vascular tissue as the disease progresses. Eventually the pith and cortex of the stem becomes dark brown.


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Leaf Spot  Alternaria sp.

Symptoms:  Numerous dark brown to black spots appear on leaves developing into concentric rings. The plant may become chlorotic and leaves may dry and drop prematurely. Stem lesions or cancers may develop.


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Flower blight-Botrytis sp.

Symptoms:  Common symptoms caused Botrytis start as small, water-soaked spots on flower petals, the spots coalesce rapidly, affecting large portions of tissue. Infection of blossoms by Botrytis may cause premature fading and dying of petals.


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Red Mites

                       Red mites are common pests on Marigolds. Although related to insects, mites are not insects but members of the arachnid class, along with spiders and ticks. Red mites are the most common and ubiquitous of all pests in the garden and farm.

Symptoms: Mites cause damage by sucking cell contents from leaves and petals. A small number of mites are not usually reason for concern, but very high population (levels high enough to show visible damage to leaves) can be damaging to plants. At first, the damage shows up as a stippling of light dots on the leaves; sometimes the leaves take on a bronze color. As feeding continues, the leaves turn yellow and drop off. Damage is compounded by water stress.


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Abnormal flower shape. Trace element deficiency- Calcium & Boron.

Symptoms :  Abnormal flower shape

Solutions :   Calcium, Boron and Potassium are crucial for ensuring proper flower development. Bud abortion indicates deficiency of these Nutrients. Excessive use of ammonium nitrate delays or decreases bud set.




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