Citrus tristeza virus

What you see

Slow overall decline: leaves yellow along the veins, growth is stunted, fruit is small and the tree may collapse suddenly in a hot spell. On sour orange rootstock a distinctive honeycomb pitting appears in the wood just below the graft.

Conditions

Spread by aphids, chiefly the brown citrus aphid and melon aphid, and by grafting with infected budwood. It is the reason sour orange rootstock is no longer used commercially in most of Iberia.

Treatment

There is no treatment. An infected tree stays infected. Manage aphids to slow spread to neighbouring trees and plan replacement.

Prevention

Buy certified virus-free nursery trees on tolerant rootstock. Never graft with budwood of unknown origin. Control aphids on the new flush.

Months: March, April, May, September, October

Plants

Orange, Lemon, Tangerine, Lime, Grapefruit

Remedies

Insecticidal soap spray, Encourage predators, Horticultural oil (white oil)

The thing people get wrong

Tristeza killed tens of millions of trees across the Mediterranean and South America, and it did it through a rootstock choice rather than through neglect. For a home grower the practical lesson is narrow but important: where your citrus came from matters more than anything you will ever do to it. A certified tree on a tolerant rootstock is worth several times a cheap unlabelled one.