Disease is a condition that can afflict most crops grown through the Farming skill.
When a healthy crop ends a growth cycle, there is a chance it may become diseased. While diseased, the crop stops growing and does not advance to the next stage. Crops do not recover from disease on their own. If the disease is not cured, the crop dies at the end of the diseased cycle. Dead crops require use of a spade to dig up their remains before planting another crop in the patch.
Players may treat plants in diseased herb, flower, allotment, hops, belladonna, cactus, mushroom, and jade vine patches with plant cure to restore the crop to health. Doing so may let the crop advance to the next growth stage normally upon the end of the cycle, although it is possible that it may become diseased again. For diseased trees and bushes, the player may use secateurs on the plant to trim the diseased branch and restore the crop to health. Alternatively, if a player has access to the Lunar Magic spellbook they may use the Cure Plant spell instead, which is substantially more expensive but may save the player valuable inventory space during a crop run.
Crops grow in real-time, so they may become diseased when a player is offline. In addition, crops that have been cured of disease may become afflicted once again. Fully grown crops will not become diseased.
Players may purchase plant cure from a Farming shop, but it is usually both more convenient and less expensive to purchase it from the nearest farmer.
Reducing disease risk
Treating a farming patch with compost, supercompost or ultracompost before planting a crop reduces the chance of disease during all growth cycles. The general risk of a plant becoming diseased without any treatment remains unknown and may vary depending on the crop and even patch, but supercompost seems to reduce the risk of disease to roughly 10% for many types of crops.
If a player forgets to treat a farming patch, the expensive but useful Fertile Soil spell may be used to treat the patch with supercompost both before and after planting a seed or sapling. Supercompost can also be used before or after.
An amulet of nature alerts a player to disease if worn, and in addition offers the option of being directly teleported to the infected crop. Both amulets may also be rubbed to check whether or not a plant is still healthy.
Eliminating disease risk
Watering allotment, flower, and hops patches with a watering can eliminates the risk of disease occurring at the end of that growth cycle. During the next growth cycle, the plant moves from being watered back to normal and becomes at risk for disease once more, unless it is watered again. Only allotment, flower, and hops patches may be watered.
Planting different flowers or a scarecrow provides protection from disease to a variety of crops in allotment patches once the flower is fully grown.
Otherwise, the only way to eliminate disease risk entirely is to pay one of the farmers near the farming patch to watch over it and ensure that it grows to completion. Payment must be in the exact form requested. For instance, a farmer does not accept 5 apples in lieu of a basket of apples. However, farmers do accept noted payment. Note that farmers require separate payment for each allotment patch.
Gaining 50% favour in the Hosidius House of favour, will eliminate the disease risk entirely of the Hosidius allotment (including the herb) patches.
The belladonna, mushroom, do not have farmers available to oversee them, however. Herb patches cannot be watered, and despite farmers overlooking the allotment patch, they do not accept payment for either the flower or herb patches.
Poison ivy bushes are immune to disease. Farmers will not accept payment to watch over a poison ivy bush. The special herb patch received by completing My Arm's Big Adventure is immune to disease, although yields may be increased by treating it with super/ultracompost.
With the elite tier of the Falador Diary complete, the tree patch in Falador Park will no longer become diseased.