Amaryllis: Complete Care Guide

Disease caused by fungus-like organisms (oomycetes) that live in soil and can survive for years. It affects roots, stem, and crown of plants, being especially severe in waterlogged or poorly drained soils. It is the second most common cause of root rot in trees and shrubs.

Leaf spot is a common fungal disease caused by various pathogens including Alternaria, Ascochyta, Colletotrichum, Septoria, and Venturia. It primarily affects leaves, causing discolored spots that can lead to premature leaf drop if left untreated.

Gray mold, caused by the fungus Botrytis cinerea, is a widespread necrotrophic pathogen affecting over 1,400 plant species. It thrives in cool, humid conditions and attacks weakened or aging plant tissues, causing soft rot and characteristic gray fuzzy growth.

Southern blight is a devastating soilborne fungal disease caused by Athelia rolfsii (formerly Sclerotium rolfsii), affecting over 500 plant species including vegetables, ornamentals, and fruit crops. The fungus survives in soil through resting structures called sclerotia that resemble mustard seeds and can remain viable for years.

Anthracnose is a fungal disease caused by fungi in the genus Colletotrichum that affects many plants, including vegetables, fruits, and trees. The disease thrives in cool, wet conditions, causing dark, sunken lesions on leaves, stems, flowers, and fruits.

Powdery mildew is a common fungal disease caused by various fungi species including Erysiphe, Podosphaera, Oïdium, and Leveillula. It affects over 10,000 plant species worldwide. The disease thrives in warm, dry climates with high humidity and appears as a distinctive white powdery coating on plant surfaces.

Bacterial soft rot is a destructive plant disease caused primarily by bacteria from the genera Pectobacterium (formerly Erwinia) and Dickeya. These bacteria produce enzymes that break down plant cell walls, causing rapid and foul-smelling tissue decomposition. It mainly affects succulent tissues such as tubers, fruits, stems, and bulbs, being especially problematic in warm and humid conditions.

Bacterial leaf spot is a plant disease caused by bacteria in the Xanthomonas and Pseudomonas genera that affects various ornamental and edible plants. The bacteria infect leaves through wounds or natural openings, causing characteristic lesions that can lead to premature leaf drop and plant weakening.

Mosaic virus is a group of plant viruses that cause mottled, patchy patterns on leaves and can affect a wide variety of plants. The virus creates characteristic yellow, white, and green mosaic patterns, often accompanied by stunted growth and deformed plant parts. This highly contagious disease spreads rapidly through insect vectors and contaminated tools.

Tomato Spotted Wilt Virus (TSWV) is one of the most devastating viral diseases affecting over 1,000 plant species across 85 families. It is transmitted by thrips and cannot be cured once a plant is infected. The virus causes severe stunting, bronzing of leaves, necrotic spots, and significant yield losses. Early detection and removal of infected plants is critical to prevent spread.

Mealybugs are small, soft-bodied insects covered with a white, waxy, cottony material. They are common pests of houseplants and outdoor plants in mild climates. These sap-sucking insects feed on plant tissue, causing damage, stunted growth, and can lead to plant death if left untreated. They produce sticky honeydew which attracts sooty mold.

Spider mites are tiny arachnids (less than 1/20 inch long) related to spiders and ticks that feed on plant sap. They thrive in hot, dry conditions and can cause significant damage to ornamental and vegetable plants. During severe infestations, crop losses can reach 14% or higher as these pests disrupt vital plant processes including photosynthesis, carbon dioxide absorption, and transpiration.

Aphids are small, soft-bodied, pear-shaped insects (1/16 to 1/8 inch long) that feed by sucking nutrient-rich sap from plants. They reproduce rapidly and can quickly weaken plants, causing distorted growth and transmitting plant viruses. Aphids come in various colors including green, black, red, yellow, brown, and gray. They secrete honeydew, a sticky substance that attracts ants and encourages sooty mold growth.

Thrips are tiny cigar-shaped insects (1/25-inch long) that damage plants by sucking plant juices and scraping at fruits, flowers, and leaves. With over 6,000 species and rapid reproduction (lifecycle as short as 14 days), they can quickly infest plants and transmit viruses like tomato spotted wilt virus.

Scale insects are small sap-sucking pests that appear as brown, shell-like bumps on plant stems and leaves. There are over 25 species, divided into armored (hard) and unarmored (soft) scales. They feed by piercing plant tissue and extracting sap, which weakens the plant and can lead to yellowing, stunted growth, and even death if left untreated. They also excrete honeydew, which attracts ants and promotes sooty mold growth.

Slugs and snails are mollusks that feed on plant tissue, causing irregular holes in leaves and damage to young seedlings. They are most active at night and in moist conditions, leaving characteristic silvery slime trails. These pests can quickly devastate gardens, especially during wet seasons.

Fungus gnats are small, gray-to-black mosquito-like insects (1/8 to 1/10 inches long) commonly found in indoor plants. Adult gnats are mostly a nuisance, but their larvae feed on plant roots and organic matter in soil, potentially causing serious damage to young or vulnerable plants. The larvae are translucent white with distinctive black heads and can leave slime trails on the soil surface in heavy infestations.

Nitrogen deficiency occurs when plants lack sufficient nitrogen, an essential macronutrient needed for chlorophyll production and overall growth. This deficiency typically manifests as yellowing leaves, starting with older foliage and progressing to newer growth if left untreated.

Potassium deficiency is a nutritional disorder that affects a plant's ability to regulate stomatal opening and closing, resulting in characteristic leaf edge burn. Potassium is a mobile nutrient, so symptoms first appear on older, lower leaves.

Magnesium deficiency is a nutrient disorder characterized by interveinal chlorosis, where leaf tissue between veins turns yellow while the veins remain green. This deficiency affects older leaves first as magnesium is a mobile nutrient that plants relocate to support new growth. Magnesium is essential for chlorophyll production and photosynthesis, making this deficiency critical for plant health.

Iron deficiency, commonly known as iron chlorosis, is a nutrient deficiency disorder where plants cannot access sufficient iron from the soil. While iron is typically abundant in soil, various soil conditions can limit plant uptake, resulting in characteristic yellowing of leaves while veins remain green.

Overwatering occurs when plants receive too much water, depriving roots of oxygen and causing root rot. This environmental stress is one of the most common causes of houseplant death, as waterlogged soil prevents roots from breathing and functioning properly.

Underwatering or drought stress is a physiological disorder that occurs when the amount of water a plant loses through transpiration exceeds the amount its roots can absorb from the soil. This leads to cellular dehydration and various visible symptoms that can compromise plant health and productivity.

Root-bound, also called pot-bound, is a common environmental condition that occurs when a plant's roots have outgrown their container. The roots become so densely packed that they circle around the root ball and cannot expand properly. This restricts the plant's ability to absorb water and nutrients, leading to stunted growth and declining health. Unlike diseases, being root-bound is not contagious and is entirely preventable through proper container management and regular repotting.

Cold damage, also known as frost injury, occurs when plants are exposed to freezing or near-freezing temperatures. This environmental stress can cause cellular damage as ice crystals form within plant tissues, rupturing cells and disrupting normal plant functions. Chilling injury can also occur in sensitive species at temperatures between 32-55°F (0-10°C), even without actual freezing.

Heat stress occurs when plants are exposed to excessively high temperatures, typically above 85-90°F (29-32°C), causing physiological damage and compromising vital processes such as photosynthesis and transpiration.

Low light stress, also known as etiolation, occurs when plants do not receive adequate light for proper growth and development. This leads to abnormal growth patterns characterized by elongated stems, pale leaves, and weakened overall structure as the plant attempts to reach toward available light sources.

Sunburn or sun scorch is an environmental condition that occurs when plants are exposed to intense, direct sunlight beyond their tolerance level. This causes the breakdown of chlorophyll in the leaves, resulting in bleached, dried, and damaged foliage. The damage can happen rapidly, sometimes within just a few hours of exposure.

Transplant shock is a stress response that occurs when plants are abruptly moved from one environment to another. This environmental condition affects plants during repotting, moving between indoor/outdoor locations, or transplanting from nursery pots to gardens. Root damage during the move is the primary cause, making it nearly impossible to completely avoid some degree of stress.

Fertilizer burn is a condition caused by applying excessive fertilizer to plants. The salts in fertilizer draw moisture out of plant tissues, leading to scorched foliage, root damage, and overall plant stress. This environmental condition is not contagious and can be reversed with proper treatment.

Salt buildup (also called salt accumulation or fertilizer salt deposits) is an environmental condition where mineral salts accumulate in the soil over time, creating a toxic environment for plant roots. The most visible sign is a white or yellowish crusty layer on the soil surface or around pot edges.

Poor air circulation is an environmental stress condition that occurs when plants lack adequate airflow around their foliage and stems. Stagnant air creates a microenvironment that promotes moisture buildup, depletes available CO2, and weakens plant defenses against fungal diseases and pests. This is especially common with densely packed indoor plants or plants placed in corners with limited ventilation.

Low humidity stress occurs when indoor air becomes too dry, causing plants to lose moisture faster than they can absorb it through their roots. This is especially common during winter heating periods, near radiators and heating vents, or in air-conditioned spaces. Tropical plants are particularly susceptible to low humidity damage.