i have been shopping at nurseries around southern California for ten years now and i have learned that starting your garden with proper planning and care is the best way to insure success, or at least give you the best chance at success, conversely making some easily avoidable mistakes can set you up for failure and headaches down the road. Let's discuss some of the things you want to avoid when shopping for plant starts or seedlings at your local nursery. Disease and insects. Just like one child at school with lice or the flu can infect the whole class, plants with disease or infested with insects can contaminated an entire garden. Often insidiously.
Here are some common diseases and insects you will likely encounter with close inspection.
Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. It is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this symptom are called blights. Several notable examples are:
On leaf tissue, symptoms of blight are the initial appearance of lesions which rapidly engulf surrounding tissue. However, leaf spot may, in advanced stages, expand to kill entire areas of leaf tissue and thus exhibit blight symptoms.
Blights are often named after their causative agent, for example Colletotrichum blight is named after the fungi Colletotrichum capsici, and Phytophthora blight is named after the water mold Phytophthora parasitica.
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales, with Podosphaera xanthii (a.k.a. Sphaerotheca fuliginea) being the most commonly reported cause. Erysiphe cichoracearum was formerly reported to be the primary causal organism throughout most of the world. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
Powdery mildew grows well in environments with high humidity and moderate temperatures. In an agricultural setting, the pathogen can be controlled using chemical methods, genetic resistance, and careful farming methods. It is important to be aware of powdery mildew and its management as the resulting disease can significantly reduce crop yields. Greenhouses provide an ideal moist, temperate environment for the spread of the disease.
Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to Peronosporaceae. In commercial agriculture, they are a particular problem for growers of crucifers, grapes and vegetables that grow on vines. The prime example is Peronospora farinosa featured in NCBI-Taxonomy and HYP3. This pathogen does not produce survival structures in the northern states of the United States, and overwinters as live mildew colonies in Gulf Coast states. It progresses northward with cucurbit production each spring. Yield loss associated with downy mildew is most likely related to soft rots that occur after plant canopies collapse and sunburn occurs on fruit. Cucurbit downy mildew only affects leaves of cucurbit plants.
Root rot is a condition found in both indoor and outdoor plants, although more common in indoor plants with poor drainage. As the name states, the roots of the plant rot. Usually, this is a result of overwatering. In houseplants, it is a very common problem, and is slightly less common in outdoor plants. In both indoor and outdoor plants, it is usually lethal and there is no effective treatment.
The excess water makes it very difficult for the roots to get the air that they need, causing them to decay. To avoid root rot, it is best to only water plants when the soil becomes dry, and to put the plant in a well-drained pot. Using a heavy soil, such as one dug up from outdoors can also cause root rot.
Many cases of root rot are caused by members of the water mould genus Phytophthora; perhaps the most aggressive is P. cinnamomi. Spores from root rot causing agents do contaminate other plants, but the rot cannot take hold unless there is adequate moisture. Spores are not only airborne, but are also carried by insects and other arthropods in the soil.
A plant with root rot will not normally survive, but can often be propagated so it will not be lost completely. Plants with root rot should be removed and destroyed.
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies, or whiteflies (not to be confused with "jumping plant lice" or true whiteflies), are small sap-sucking insects, and members of the superfamily Aphidoidea. Many species are green but other commonly occurring species may be white and wooly, brown, or black. Aphids are among the most destructive insect pests on cultivated plants in temperate regions. They are capable of extremely rapid increase in numbers by asexual reproduction. The damage they do to plants has made them enemies of farmers and gardeners around the world. From a zoological standpoint they are a highly successful group of organisms.
About 4,400 species are known, all included in the family Aphididae. Around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in length from 1 to 10 millimetres (0.04 to 0.39 in).
Natural enemies include predatory ladybugs, hoverfly larvae, parasitic wasps, aphid midge larvae, crab spiders, lacewings, and entomopathogenic fungi such as Lecanicillium lecanii and the Entomophthorales.
Whiteflies are small Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described.
leaf miners are the larva of an insect that lives in and eats the leaf tissue of plants. The vast majority of leaf-mining insects are moths (Lepidoptera), sawflies (Symphyta, a type of wasp) and flies (Diptera), though some beetles also exhibit this behavior.
Like woodboring beetles, leaf miners are protected from many predators and plant defenses by feeding within the tissues of the leaves themselves, selectively eating only the layers that have the least amount of cellulose. When attacking Quercus robur (English oak), they also selectively feed on tissues containing lower levels of tannin, a deterrent chemical produced in great abundance by the tree.
The precise pattern formed by the feeding tunnel is very often diagnostic for which kind of insect is responsible, sometimes even to specific level. The mine often contains frass, or droppings, and the pattern of frass deposition, mine shape and host plant identity are useful to determine the species of leaf miner. A few mining insects utilise other parts of a plant, such as the surface of a fruit.
It has been suggested that some patterns of leaf variegation may be part of a defensive strategy employed by plants to deceive adult leaf miners into thinking that a leaf has already been preyed upon.
spider mites are members of the Acari (mite) family Tetranychidae, which includes about 1,200 species. They generally live on the undersides of leaves of plants, where they may spin protective silk webs, and they can cause damage by puncturing the plant cells to feed. Spider mites are known to feed on several hundred species of plants.
These are just a few of the most common diseases and insects you will encounter during inspection of your potential plants. Remember an ounce of prevention is worth a pound of cure, not only will using techniques like this save you from creating and uphill battle for you in the garden but it will also reduce or eliminate the need for harmful chemical pesticides, funguscides and algicides.