In our continued look into what can go wrong in Aquaponics, this post looks into the 5 common plant diseases and deficiencies. We'll also touch on how to prevent them from becoming a problem in your system and, if need be, treat them once you detect something is wrong. We look at iron and magnesium deficiencies and three diseases: powdery mildew, Lettuce Mosaic Virus, and Tomato Spotted Wilt Virus. Click to continue reading!
1. Iron Deficiency
Similar to a magnesium deficiency, the main symptom of an iron deficiency is chlorosis of plant leaves. Understanding the basic differences can be done using an eye-test. In iron deficient plants, new growth will show complete chlorosis while mature leaves will remain green in the veins. Plants need iron to both photosynthesize and uptake nitrogen and phosphorous through their roots. The tough part about iron is that it there is usually not enough of it in fish food to support plant life, so it must always be added supplementally.
The best way to prevent iron deficiencies is to take regular iron tests of your water as you establish your system and understand how quickly your plants uptake iron. Iron test reagent kits can be purchased from your local jacuzzi store and can be found easily online. Once you know how quickly your iron drops, you can create a schedule of how you add Chelated iron, an iron supplement, to your system. From our research it seems like once your iron drops below 1.5ppm, you need to add chelated iron. The amount you add depends on your system size. Be very cautious when adding chelated iron to your system as over-doing it will impede your plants ability to take up nutrients. The best way to treat and prevent iron deficiency is to carefully test and discover the ratio of added chelated iron to rise in ppm. Once you have that ratio down, you can feel comfortable both adding regular doses of chelated iron and treating any observed iron deficiencies.
On another note, it is one of our longterm goals to offer an iron single ion sensor to OsmoBot.
2. Powdery Mildew
Gray growths on the plants' leaves or fruit. The main contributing factor for powdery mildew is high humidity. When standing water is allowed to sit on the plants leaves, mold and fungal spores can land and start to grow. This can be an especially large problem in "closed systems" that have little ventilation and connection to the outside world. Thus, avoiding mold and fungi on your plants is a main reason for tracking humidity and ensuring that your greenhouse has the proper ventilation.
The best treatments for powdery mildew are preventative. First, keep track of your humidity and ensure that it remains in check. Develop the proper ventilation habits or make the necessary adaptations to your greenhouse design to keep your relative humidity within a healthy range. Also, if you are growing commercially and are having this problem, you may want to revisit your sanitation policies for you and your staff. You and your staff are a great way for outside molds and fungi to get into your greenhouse. Once you have discovered powdery mildew there are a number of natural foliar sprays that seem to work for people. Powdery mildew and potassium don't seem to mix, so foliar sprays that are high in potassium can be very effective. Kelp extract is a great additive for potassium. Checkout this community forum page for more ideas on how to control powdery mildew in your aquaponics systems: http://community.theaquaponicsource.com/forum/topics/powdery-mildew
3. Lettuce Mosaic Virus
Yellowing, stunting, distortion, failure to head, and breaks or tears in leaves. The Lettuce Mosaic Virus can be introduced into your system from infected seed. When a mother plant is infected about 1-10% of the offspring seed will carry the virus. The problem for your aquaponics system is that pests, such as aphids can carry the disease from plant to plant, thus, if unchecked the Lettuce Mosaic Virus can spread to your entire crop, leading to complete loss. Luckily the virus poses no harm to humans, but it makes the plants very unattractive and nutrient deficient.
Unfortunately there are no treatments for Lettuce Mosaic Virus. The best way to prevent it is to have a trusted seed source of Mosaic Tested Seeds (MT0) and watch your seedlings for uncharacteristic behavior, such as misshapen first leaves and stunting. Remove infected plants from your system, hot compost them to kill the virus, and monitor the surrounding plants closely over the next 10-15 days to watch for first symptoms of the virus in other plants. Also spray the surrounding plants with an anti-aphid foliar spray to limit transmission.
4. Tomato Spotted Wilt Virus
Most common in tomatoes, but also appearing in peppers and lettuces, Tomato Spotted Wilt Virus is characterized by inward cupping of the leaves in younger plants and dark streaks down the main stem in more mature plants. The fruit can be deformed showing uneven ripening and raised bumps on the surface. Infection is spread by thrips and can occur when an infected leaf rubs against a healthy one.
Unfortunately there is no treatment for Tomato Spotted Wilt Virus. Once you detect the virus, remove the plant immediately and hot compost it to eliminate the virus. Be careful to not rub the plant against others on your way out and wash your clothes before returning to the greenhouse. Then, if the plants surrounding it look healthy, use a natural anti-thrip foliar spray to reduce the likelihood of further transmission in your greenhouse and watch that area closely over the next few weeks for signs of the virus having spread.
5. Magnesium Deficiency
The first sign that you have a magnesium deficiency is you will see chlorosis or a yellowing between the leaf and the vein, giving the leaf a "marbled" appearance. This happens because magnesium is a central atom in chlorophyl, so when it's running the low, the plant begins to break down the chlorophyl in old leaves to supply magnesium to the newer ones. If it goes untreated, the plant will be unable to photosynthesize at peak capacity and therefore will be stunted.
When you first notice chlorosis in your system perform a water check as it's a symptom of a number of deficiencies and you want to find the right treatment path. Once you have concluded that it is magnesium that is low, you can add Epsom salt or to your system as these will generally not be toxic to your fish. According to Aquaponic Source moderator, Vlad Jovanovic, the amount of Epsom salt to be added is as follows:
- "57.5 GRAMS OF EPSOM SALT INTO 100 US GALLONS OF WATER WILL GARNER YOU 15PPM OF MAGNESIUM. 15PPM IS ABOUT HALF (30PPM) OF THE TOTAL MG YOU WOULD WANT IN SOLUTION. SO IT'S A PRETTY LOW DOSE AND ASSUMES THERE IS SOME AMOUNT OF MG ALREADY PRESENT IN YOUR SYSTEM...HENCE THE 15PPM TARGET (AND NOT 30PPM)"