Lemon Tree Growing Conditions

• Lemon trees cannot tolerate temperatures that dip below 20 degrees Fahrenheit, and their fruits and flowers are killed in temperatures below 30 degrees. Lemon trees also need protection from damaging winds. Plant lemon trees where they receive full sunlight and get adequate drainage. Lemon trees can reach a maximum height of 20 feet and should be spaced 25 feet apart. Planting lemon trees too closely together can breed disease. Keep young lemon trees well-watered until established then cut back to one thorough watering every two weeks. Over-watering encourages pathogens.
  
  

Downy Mildew

• Downy mildew first appears as angular pale yellow spots on the upper side of the foliage then forms concentric white, gray or tan spots on the undersides. Downy mildew can also attack young shoots and fruit by forming a white coating. Downy mildew thrives in cool, moist conditions. Allow lemon trees to dry between waterings and plant them in areas that receive sufficient drainage. Don't plant them in heavy soils, such as clay that tends to retain water. Remove leaves and other areas on the tree that are badly infected to reduce mildew spread.
  
  

Giant Whitefly

• The giant whitefly, Aleurodicus dugesii, is native to Mexico and leaves spirals of white wax on the under and upper sides of leaves as the adults walk on them. Eggs are usually deposited in these white spirals. Giant whiteflies cause damage by sucking the sap from the leaves, which stunts the tree's growth, weakens it and may even kill it if the infestation is serious and unchecked. Giant whiteflies also excrete honeydew, which produces sooty mold, inhibiting the lemon tree from photosynthesizing.
  
  

Lemon Tree Fungi Control

• Copper is a broad-spectrum fungicide used for fruit trees, including lemons. It works to inactivate critical enzyme systems in the fungi. Copper is available as a dust, wettable powder, liquid or ready-to-use formula. Use copper with care because it persists indefinitely in the soil and may harm beneficial organisms. Bordeaux mix is a combination of copper sulfate and hydrated lime that acts as a fungicide and insect repellent. It's also designed for various fruit tree fungi, but it can burn plant foliage. Avoid using it when temperatures are below 50 degrees Fahrenheit.
  
  

Lemon Tree Insect Control

• Apply neem oil, a systemic pesticide that contains the chemical azadirachtin, to make the plant sap unpalatable to insects, like the giant whitefly. Even if the giant whitefly continues to feed on the lemon tree, it becomes unable to reproduce. Biological control is effective at controlling whitefly populations. Parasitic wasps sting the giant whitefly and insert an egg that develops inside the host and kills it. Female parasitic wasps also sting whiteflies and suck their body fluids. Species from the Coccinellidae, particularly Delphastus catalinae and Cryptolaemus montazorri, also feed on giant whiteflies.