ABSTRACT
Whenever the crop is terminated and all plants disposed of, the entire growing area must be sanitized to prevent carryover of pests and diseases to the next crop� Prior to pulling the crops spray them with a pesticide to kill most of the flying insects� As you remove the plants place them in large garbage bags to prevent infested plants from spreading pests and diseases� The plant debris can be taken to a garbage land fill or you can bury them in a pit outside covering it after with soil� This is the more difficult way as the pit would have to be dug to about 3 ft in depth� Making a pit could be a lot of work, especially if in the winter when the ground is partially frozen� It is best to take the plant remains to a landfill� If you are a backyard gardener and keep compost the crop debris could be composted�
Vacuum up all small leaves and so on as any plant debris left over could carry insect eggs or overwintering fungal spores� Then, spray the entire growing area with a 10% bleach solution or other disinfectant� This includes the walls, floors, and growing support trays� The growing channels, pond, pots, seedling trays, tomahooks, and plant clips should be soaked in a 10% Clorox solution for several hours�
Disinfectants are oxidizing agents that kill microorganisms� Others besides bleach you may use include “Virkon” (peroxide) and “KleenGrow” (quaternary ammonium)� Use safety equipment such as a respirator, disposable gloves, and suit when spraying these compounds as they are irritants to your skin� Never mix bleach with ammonia or acidic solutions as such combinations produce toxic chlorine gases� So, just be careful and there will be no problems! KleenGrow is registered for greenhouse and indoor crop production facilities� Thoroughly wet the surfaces� Use 1�0 oz per gallon of water or 6-8 mL of KleenGrow per liter of water for greenhouse surfaces and equipment� Always read and follow label directions precisely�
Exclude insects as much as possible with the use of screens on any intakes that bring in fresh outside air� Sanitation practices including removing any pruning debris and damaged or deformed fruit reduces diseases� After all you would not be happy living in a dirty, cluttered house so keep your plants’ living quarters clean also to assist them from becoming sick! Preventing insects from entering will reduce diseases in that many insects suck on plant tissue passing on fungal spores and viruses to your plants� Sucking insects inject viruses into the plants as they rasp or enter the plant tissues with their mouthparts� These insects include aphids, mites, thrips, and whiteflies� They also carry fungal spores on their bodies and transmit them to plants as they suck the juices from the plants creating an ideal point of entry for fungal spore germination�
Prevent diseases by keeping the plants healthy with an active root system� Proper oxygenation, moisture levels, and nutrition all play an important role in healthy, vigorous plants as we discussed earlier� Good hygiene of keeping the growing area clean will reduce the presence of material that may harbor diseases� Be vigilant in recognizing any plant symptoms expressed by the presence of a disease or insect� Early detection and identification of any diseases and/or insects is the key to successful control of these ailments� There are many websites (see Appendix) that give colored pictures of pests and diseases and also recommend control measures� Use these sites for identification and always take photos for future reference�
Take into consideration that the plant symptoms may also be an expression of nutritional or environmental disorders� Plant disorders are discussed in Chapter 10�
As soon as you have determined the cause of the disease or which pest is present, take fast, corrective actions to control them to prevent their spread� Use approved chemical sprays� Seek the use of natural pesticides (bioagents)� If these are not sufficiently effective, then apply stronger ones� Do not repeatedly apply the same pesticides in future infestations; vary the type of pesticides to minimize any possible resistance build-up by the pests� An even better approach is to introduce natural predators (beneficial insects) into the crop that will eat or parasitize the pests keeping their numbers limited� These beneficial insects are available through numerous distributors and even hydroponic outlets� Once again there is a lot of information available on the Internet (see Appendix)�
When selecting varieties, as discussed in Chapter 22, you should choose resistant varieties against diseases� The use of resistant varieties will simplify and increase your success� While hydroponic growing greatly reduces the threat of disease in the substrate, it does not prevent diseases in the plant growth above the substrate� Maintaining optimum environmental conditions and controlling pests will help greatly in the prevention of diseases�
Once you think a disease is present start to identify specific areas on the plant that are affected and describe the nature of the symptoms (Figure 25�1)� Firstly, identify the area affected: leaves, flowers, fruit, growing tip, stem, crown area, or roots� It may be a combination of these� For example, if the plant wilts during the high light and temperature periods of the day, probably the roots are infected reducing water
uptake� Cut some roots to determine whether or not they are turgid and white or soft and slimy� If the latter, you know immediately there is a root problem�
Is the overall plant form stunted or dwarfed? Is the top of the plant very bushy with many small leaves and short internodes? Look for the following symptoms: deformed, wrinkled, rolled, curled, mottled, chlorotic, necrotic leaflets� Look for the presence of spots-concentric or curved, white, powdery, hair-like growth on the leaves (due to some fungi, such as powdery mildew and Botrytis)�
Cut the stem on a plant to find out whether or not the vascular tissue is clear and white or brown and soft that would indicate the presence of a disease organism� Any discoloration or softness at the collar (crown) of the plant would indicate a disease� A fruit may be deformed or have spots or lesions pointing to the presence of a disease� After describing and taking photos for future reference of these symptoms go onto websites of the Internet to find photos and descriptions of disease symptoms that may be similar to those of your plants (see Appendix)�
1� Leaf mold (Cladosporium): It starts as a small gray spot on the underside of the leaf and expands into a pale area on the upper surface� Good sanitation,
ventilation, and temperatures preventing high humidity reduce potential infection� Some effective fungicides are available�
2� Early blight (Alternaria and Septoria): Dead spots appear on leaves, attacking older leaves first� Ventilation reduces infection� Remove lower leaves as plants are lowered to increase air circulation thus creating lower relative humidity�
3� Gray mold (Botrytis): These fungal spores enter wounds� That is the reason for cutting leaves with a sharp knife or pruning shears to get a clean surface that will heal quickly� Gray mold appears as a moist rot with a fluffy gray (hairy-like) growth above the infected area� Some fungicides can control the infection at its early stage before the fungus destroys (girdles) the entire plant stem�
4� Viruses: Most greenhouse varieties have resistance or tolerance to many viruses� Reduce potential infection by controlling sucking insects that are vectors (aphids, mites, whiteflies)�
Since tomatoes, eggplants, and peppers are of the Solanaceous family, they are prone to the same diseases� Tomatoes and eggplants are of the genera Solanum and so are very closely related� This family also includes vegetables such as potatoes and some flowers�
1� Gray mold (Botrytis): This is the most prevalent disease of eggplants� Maintain optimum humidity levels through ventilation and temperature� De-leafing lower, yellowing leaves will assist in keeping the humidity near the plant base low� Make a clean break or cut at the base of the leaf petiole (where the leaf joins the stem)� Botrytis will also affect fruits, stems, and leaves� Cut the fruit during harvesting with a pruning shears or sharp knife to create a rapid healing of the wound� After flowering remove dead flowers that have not set fruit as often Botrytis quickly invades these dead tissues�
2� Stem rot (Sclerotinia): This is a fungus that infects the stem of eggplants� Treat it as for Botrytis� Practice good sanitation and ventilation�
Both gray mold and stem rot occur on peppers� Treatments are the same as for eggplants and tomatoes� A number of viruses also may infect peppers� The best step is prevention by elimination of sucking insects�
1� Powdery mildew: This is the most common disease on cucumbers� Small white spots appear on the upper leaf surface (Figure 25�2)� It spreads rapidly to nearby leaves and plants� Spots enlarge and spread to cover the entire leaf surface as the disease progresses� Proper sanitation and ventilation assist in preventing this disease� Elemental sulfur vaporized by a heater will create a cloud that can penetrate all areas within the crop� This is generally done
overnight� The best remedy for this disease is the selection of resistant or highly tolerant varieties such as Dominica, Logica, and Marillo� Powdery mildew is especially infectious under tropical, humid conditions�
2� Gray mold (Botrytis): The symptoms and controls are similar as for tomatoes� 3� Gummy stem blight (Didymella bryoniae): This disease of flowers, devel-
oping fruit, petiole, and base of the main stem is expressed as tan-colored lesions� Good ventilation and optimum relative humidity will discourage infection by this fungus� Some fungicides will arrest the infection�
4� Cucumber mosaic virus (CMV): Some strains of this virus also infect tomatoes� Affected leaves become dwarfed, long, and narrow� There is no cure, only prevention through sanitation and eradication of sucking insects� There are many cucumber cultivars now resistant to this virus� They are indicated by the code CMV after the variety name�
Lettuce is susceptible to several diseases including Botrytis, which is treated as for any of the other crops�
1� Bacterial soft rot (Erwinia carotovora): This is a bacterium� It causes rotting of the internal part of the head as it forms and also at the crown of the plant� Optimum ventilation to maintain optimum humidity levels helps in abating this disease� Sanitation between crops and during production helps to minimize any infection�
2� Lettuce big vein (Mirafiori lettuce virus): Symptoms are enlarged, clear veins of the leaves� Leaves become ruffled and malformed in appearance� Sanitation and resistant varieties are the means of prevention�
3� Powdery mildew: This disease produces the same white spots on leaves as in the case of cucumbers� Treatment is the same with vaporized elemental sulfur� Removal of the crop followed by strict sanitation is obligatory� Use resistant varieties�
Some herbs are particularly susceptible to Powdery Mildew and Botrytis. Basil is affected by bacterial soft rot, especially after harvesting when packaged� Fusarium root rot in basil can be avoided through the use of resistant varieties such as “Aroma 2” and “Nufar�” Fungal and bacterial leaf spots may occur, especially under high relative humidity or excessive moistening of leaves� Follow control measures as outlined earlier for the other crops�
Most of the pests such as aphids, larvae of caterpillars and moths, mealybugs, twospotted spider mites, thrips, and whiteflies infest all of the crops� However, some are more aggressive on certain crops than others� They are listed in order of importance under each crop� For details on the identification, life cycles, and control measures refer to websites and books listed in the Appendix such as my book Hydroponic Food Production�
Place yellow sticky traps on the overhead wires or support strings about a foot above the top of the plant to catch and monitor the presence of these pests�
1� Whiteflies: This is the most troublesome pest associated with tomatoes (Figure 25�3)� You can easily identify this insect by its white wings and body� It is most prevalent on the undersides of leaves and flies quickly when disturbed� There are beneficial insects as well as pesticides available for their control� All of those details you can get at various websites listed in the Appendix�
2� Aphids: These pests are almost always found in your backyard garden� They are green, brown, or black in color depending upon the species� Their distinguishing pear-shaped body places them apart from other insects (Figure 25�4)� There are winged and wingless forms� One prominent characteristic of their infestation on plants is the presence of “honeydew” excreted from their abdomens causing stickiness of leaves and plant parts as they suck on the plants� This liquid attracts ants, so if you encounter large ant populations around the plants it could be due to the presence of aphids� Often sooty molds (fungi) infect the leaves as a secondary organism, creating a black film on the leaves�
3� Two-spotted spider mite: Mites are related to spiders and ticks� They have four pairs of legs compared to insects that have only three pairs of legs� They have two dark-colored spots on their bodies that differentiate them from other mites (Figure 25�5)� As they suck on the leaves, small yellow spots form that eventually coalesce to give a bronze appearance to the leaves� They also produce webbing on the leaf surface as infestation increases� If not controlled when numbers are manageable, they will cause complete bleaching and death of the leaves as they suck out all the contents of the cells�
Several other mites exist that also damage greenhouse crops, carmine mites, and broad mites� These, however, are not as prevalent as the two-spotted mite� They lack the two dark spots and differ in color� The carmine mite is bright red, while the broad mite is translucent and can only be seen with a hand lens� Broad mites cause leaf and fruit deformation�
4� Thrips: These insects are especially attracted to the flowers� Their distinct feature is the presence of feathery wings (Figure 25�6)� They have rasping mouthparts that scrape the leaf surface and suck the plant sap, causing white, silvery streaks on the leaves� They, like whiteflies and aphids, also carry viruses� Thrips are more attracted to blue sticky traps�
5� Leafminers: Adult leafminers are flies yellow-black in color (Figure 25�7)� They deposit eggs in the leaves that show as white swellings� As the larvae hatch, they eat “tunnels” through the leaf between the upper and lower leaf epidermis, creating “mines�” As infestation increases, the mines coalesce resulting in large areas of damage that eventually lead to the death of the leaf� The mature larvae drop to the ground (surface of the substrate) where they pupate (go through metamorphosis to adults) within 10 days� The cycle begins all over again�
Reduce infestations by the removal of badly infected leaves and clean up any fallen leaves from the floor� If the substrate is covered with white
polyethylene to prevent the larvae from entering as they fall from the leaves, it will minimize the reproduction of the insects� This is particularly helpful if your plants are growing in pots or beds� The use of plastic wrapped slabs will restrict the infestation by breaking the life cycle�
6� Caterpillars and cutworms: These are larvae of butterflies and moths, respectively (Figure 25�8)� Their presence on crops is indicated by notches in leaves and cut stems and leaf petioles� Cutworms climb up the plants and feed at night, going back to the substrate to hide during the day� Caterpillars feed day
and night� Another tell-tale sign of their presence is the excrements on leaves where they are feeding� Some hornworms can kill an entire plant in one day or night� Look for their signs and pick them off by hand� Also, control them by spraying Dipel or Xentari weekly� Dipel and Xentari are a bacterium (Bacillus thuringiensis)� This product is very safe and is a biological control agent�
1� Whiteflies: These are very common on eggplants� Treatment is as for tomatoes�
2� Aphids: The same types of aphids and their control as for tomatoes applies� 3� Two-spotted spider mite: Once again their control is the same as for
tomatoes� 4� Mealybugs: These are notorious on peppers, eggplants, and basil� They have
a very characteristic appearance of forming a white wax-like substance covering their bodies (Figure 25�9)� It is powder filaments and projections or plates� These filaments protect the insect from contact with many sprays� When using a spray, add a sticker to breakdown the surface tension of the filaments so that the pesticide can contact the insect� There are a few beneficial insects that prey on the pests�
5� Caterpillars and cutworms: Look for the same signs as for tomatoes and control them in the same manner�
1� Mealybugs: The worst enemy of peppers and the most difficult to control is the mealybug (Figure 25�9)� Peppers are also susceptible to whiteflies, aphids, thrips, mites, caterpillars, and cutworms in that order of importance� But these are all easier to control than the mealybugs� Mealybugs cause secretion on the leaves and fruit as they suck the juices from the plants� This sticky substance attracts ants and initiates secondary fungus infection such as sooty mold�
Control mealybugs as soon as they are sighted at an early stage before they form their protective waxy coating� At this early stage use natural pesticides such as M-Pede, Azatin, and BotaniGard� Infestation progresses very rapidly and will cause leaves to senesce (turn yellow), die, and fall� Remove any heavily infested leaves and bury them�
2� Broad mites: Broad mites are translucent and much smaller than the carmine or two-spotted spider mite� The first signs of damage are the curling of young leaves and their becoming brittle� Soon after the initial plant responds, the broad mites will kill the growing point of the plants (Figure 25�10)� Once the growing points are damaged to the extent that they dry and break off, the plants are lost as they do not easily form new side shoots� Broad mites also cause scarring of fruit and its deformation� The fruit is not useable at that stage of symptom development�
Fortunately, they can be controlled by use of Azatin, Neemix, and Abamectin� There are also a number of predatory mites that keep the broad mites in check�
3� Thrips: These are more common in peppers than in tomatoes or eggplants� Again monitor them with the sticky cards and control them with natural pesticides and beneficial insects�
4� Caterpillars and cutworms: These not only chew holes in the leaves, but also may cut through the stems and eat their way into the fruit at the stem end and then devour the fruit from the inside until it falls from the vines�
1� Mites: All three of the mites mentioned earlier love to feed on cucumbers� The two-spotted red spider mite is most common, but carmine and broad mites also attack cucumbers� Broad mites cause the death of the growing point and damage fruit with the appearance of many small white spots that also cause deformation of the fruit� However, malformation is not as severe as with the fruit of peppers� Both beneficial predatory mites and some midges feed on these pests�
Mites are probably the worst pest of strawberries causing damage on the fruit and leaves with webbing as the infestation progresses�
2� Whiteflies: Always check the undersides of leaves as that is generally where infestation begins� Control is as for tomatoes and other crops�
3� Mealybugs: Mealybugs probably prefer peppers, eggplants, basil, cucumbers, and tomatoes in that order� At least I have found that in my experience over the years!
