How to treat root rot in purple shamrock? Symptom identification and treatment methods

1. Disease symptoms

Root rot damages the root system and bulbs of purple shamrock. Affected plants show wilting under sunlight during the day, and recover somewhat from night to early morning. The initial symptoms are that the leaves of purple shamrock show a state similar to nutrient deficiency and loss of purple color; the roots appear shrunken; there are few fibrous roots, which are pale yellow-brown; the main root shows no obvious symptoms. As the disease worsens, the plant's growth becomes increasingly poor, the leaves begin to turn yellow and wither, the fibrous roots rot completely, and the main root turns dark brown and gradually rots as well; after squeezing, the root cortex peels off very easily; dark brown mold layers and gum-like fluid are sometimes visible at the base of the bulbs. Finally, as water deficiency in the plant worsens, all the leaves of purple shamrock wilt, and the plant dies. This disease is not easy to detect in its early stages.

2. Disease occurrence pattern

The pathogen overwinters in the soil and on diseased plant residues. The pathogen invades the interior of purple shamrock through root wounds, then produces conidia in the diseased parts, which spread and proliferate with the aid of rainwater or irrigation water, causing secondary infection. A high-temperature and high-humidity environment favors the onset of the disease. In addition to environmental conditions, the occurrence of the disease is closely related to cultivation and management. In continuous cropping land where the soil has not been disinfected, where there is local low-lying water accumulation, where undecomposed fertilizer is used, where underground pests occur frequently, or where agricultural operations cause root damage, the disease tends to be relatively severe. Generally, it occurs more severely in high-temperature seasons, and is also extremely likely to occur when soil moisture content is high.

3. Control measures

(1) Agricultural control:

Clean the cultivation site promptly, fertilize and water scientifically, prevent flooding irrigation, and keep soil moisture moderate. Before cultivating purple shamrock, spray the substrate alternately with several fungicides several times to disinfect it well. Pentachloronitrobenzene or formalin can be used for disinfection. Pull out and destroy diseased plants promptly when found. The root rot pathogen is an anaerobic bacterium. After purple shamrock is planted, loosening the soil once every 3-5d to enhance soil aeration is an effective control measure.

(2) Chemical control:

In the early stage of the disease, spray or drench the roots with 50% thiophanate-methyl 500-fold solution, 50% carbendazim 500-fold solution, etc. After the disease occurs, you can use 50% tecloftalam 700-fold solution, 50% thiophanate-methyl 1000-fold solution, 65% dexon 600-800-fold solution, 75% chlorothalonil 600-fold solution and other agents to drench the roots or spray.

Symptoms and treatment of wild slug damage on purple shamrock

1. Morphological characteristics

The wild slug belongs to the order Stylommatophora, family Limacidae, also known as the slug. The adult is spindle-shaped, 20-25mm long and 4-6mm wide; the body surface is smooth, without an outer shell, dark gray, yellowish white, or grayish red; there are two pairs of tentacles, dark black, with the eyes at the tips of the posterior tentacles; the front part of the back has a mantle, with curled edges, bearing obvious concentric circular growth lines, and the mucus is colorless; the eggs are white and transparent, gelatinous and oval, gathered in clusters within egg capsules; newly hatched juveniles are pale brown and resemble the adult in body form.

2. Occurrence pattern

The wild slug occurs in 1-2 generations per year, overwintering as adults and juveniles under moist soil at the plant roots, and causes more severe damage in spring and autumn. Air temperatures of 11.5-18.5°C and soil moisture content of 20-30% favor its reproduction. During the day, the wild slug hides at the roots of purple shamrock and in soil crevices, and at night it crawls out onto the ground to activity, harming the growth of purple shamrock. It has a strong tolerance for starvation and can refrain from eating or moving under food shortage or unfavorable conditions. The wild slug prefers dark and humid environments, and damage is most severe especially in the corners of greenhouses in spring and in environments with high plant density and poor ventilation. Its feeding activity is most intense from evening to just before dawn the next day. When the wild slug encounters unfavorable environments such as dryness or irritating odors, it can quickly contract its abdominal foot into the shell and secrete mucus, forming a liquid membrane outside the shell opening to protect itself through the unfavorable environment. However, it has a strong tendency toward sugar. The wild slug fears light, and under strong sunlight it will die within 2-3h.

3. Damage characteristics

The wild slug has omnivorous feeding habits and prefers to eat the leaves and petioles of purple shamrock, forming irregular notches, holes, or dead seedlings. Affected leaves are scraped and contaminated by the feces left behind, losing their ornamental value. The body of the wild slug carries various pathogens, and the wounds caused by its biting become channels for pathogen invasion, which can lead to fungal infection and cause the leaves to rot.

4. Control measures

The wild slug is highly concealed, and its body surface secretes a large amount of mucus, so the liquid medicine cannot easily reach the pest body directly. General insecticides are difficult to make effective, making it a relatively difficult pest to control on potted purple shamrock.

(1) Agricultural control:

Dig drainage ditches well in greenhouses, pay attention to drainage, lower the groundwater level, and remove weeds promptly. Carry out intertillage and weeding on sunny days to expose eggs on the soil surface so they die on their own. Spread lime powder or plant ash at the edges of outdoor sites where purple shamrock is placed to reduce humidity and create an environment unfavorable for wild slug activity; after the wild slug crawls over it, its body will die from water loss.

(2) Chemical control:

During the peak occurrence period of the wild slug, spray ammonium bicarbonate 100-fold solution, 40% slug enemy concentrated aqueous solution 100-fold solution, and other agents. Because slugs are inactive during the day, the liquid medicine cannot easily be sprayed onto the bodies of wild slugs, so the general control effect is not ideal. Therefore, before carrying out chemical control, water the ground in the greenhouse and the inside of flower pots to increase environmental humidity so as to facilitate slug activity, and apply the pesticide in the evening. In order to achieve sustained and effective control, carry out control 2-3 times consecutively. Taking advantage of the wild slug's habit of being attracted to fragrance, use metaldehyde to prepare toxic bait containing 4% active ingredient in oil cake powder or cornmeal, and scatter it in the evening on the ground between flower pots or at the edges of flower pots to trap and kill them. Chemical control experiments show that the control effect can also reach more than 85%.

The prevention and control of diseases and pests on purple shamrock is a complex task with strong comprehensiveness. It should be based on agricultural practices, with prevention as the main approach, eliminating the sources of diseases and pests, and combining physical methods, chemical agents, and biological natural enemies for integrated management. Follow the principle of "treat early, treat small, treat thoroughly", and eliminate diseases and pests at the initial stage of occurrence, rather than waiting until purple shamrock has suffered severe damage before treating it.

Is Oxalis griffithii a flowering plant? Pictures and brief introduction of Oxalis griffithii

Chinese name: Oxalis griffithii

Alternative name: purple shamrock

Latin scientific name: Oxalis griffithii Edgew. et Hook.f.

Family and genus: Oxalidaceae, Oxalis

Origin and distribution: China

Oxalis griffithii has a peculiar leaf shape, deep purple leaf color, and small white-pink flowers, creating a strong color contrast that is very eye-catching. It is mainly propagated by division and sowing. Division can be carried out throughout the year, with division in April-May in spring being best. It prefers a warm and humid environment. It grows vigorously in fertile and moist soil and is relatively cold-tolerant. It is suitable for potted cultivation, and is very suitable as a groundcover plant in shady and humid areas in gardens.