Disease (Farming)

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This article is about the condition that affects planted crops. For the condition that affects players, see Disease.
A diseased redwood tree.

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, and die at the end of the diseased cycle if left uncured. Dead crops yield no experience and 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, bush, hops, tree, fruit tree, hardwood tree, spirit, celastrus, belladonna, cactus, and mushroom 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.

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.

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. Crops cannot become diseased in the first growth stage (i.e. immediately after the seed has been planted), and fully grown crops will not become diseased.

An amulet of nature alerts a player to disease if worn, and may also be rubbed to check whether or not a plant is still healthy.

Reducing disease risk

Each crop type has a predetermined probability of becoming diseased each crop window. Treating a farming patch with compost, supercompost or ultracompost before (or immediately after) planting a crop reduces the chance of disease during all growth cycles by 50%, 80% or 90%, respectively, rounded down to the nearest 1/128th. If an Iasor is planted and alive, disease risk of all crops is reduced by a further 80%[1], to a minimum chance of 1/128 per growth cycle. The risk of a plant becoming diseased without any treatment varies depending on the crop (and in some cases the specific patch). These rates are unknown, except for the following crops:[2]

Plant Disease Chance per Cycle[?] with Compost with Supercompost with Ultracompost with Ultracompost and Iasor
All Fruit trees 18/128 (~14.1%) 9/128 (~7%) 4/128 (~3.1%) 2/128 (~1.6%) 1/128 (~0.8%)
Maple Trees 13/128 (~10.2%) 7/128 (~5.5%) 3/128 (~2.3%) 2/128 (~1.6%) 1/128 (~0.8%)
Magic Tree 9/128 (~7%) 5/128 (~3.9%) 2/128 (~1.6%) 1/128 (0.8%) 1/128 (~0.8%)
All Herb 27/128 (~21.1%) 14/128 (~10.9%) 6/128 (~4.7%) 3/128 (~2.3%) 1/128 (~0.8%)

The probability a crop will fully grow without getting diseased and dying is ${\displaystyle (1-P)^{n-1}}$, where ${\displaystyle P}$ is the probability found in the above table and ${\displaystyle n}$ is the number of growth cycles the crop requires to fully grow. For example, fruit trees require 6 growth cycles, and if ultracompost is used, the tree has a ${\displaystyle \left(1-{\frac {2}{128}}\right)^{6-1}=92.43\%}$ chance of fully growing without becoming diseased and dying.

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 (or ultracompost if you have previously read the Ash covered tome) both before and after planting a seed or sapling. Supercompost and ultracompost can also be used before or after.

Watering allotment, flower, and hops patches with a watering can reduces the risk of disease occurring at the end of that growth cycle.[3] During the next growth cycle, the plant changes from being watered back to normal and has a higher risk for disease once more, unless it is watered again. Only allotment, flower, and hops patches may be watered.

Eliminating disease risk

Planting different flowers or a scarecrow provides protection from disease to a variety of crops in allotment patches once the flower is fully grown.

The special herb patches unlocked by completing My Arm's Big Adventure and Making Friends with My Arm are immune to disease, although herb yields may still be increased by treating the patches with super/ultracompost.

Gaining 50% Hosidius favour will eliminate the disease risk entirely of the Hosidius allotment, herb, and flower patches.

With the elite tier of the Falador Diary complete, the tree patch in Falador Park will no longer become diseased.

Otherwise, the only way to eliminate disease risk entirely from all other patches 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.

The belladonna and mushroom patches do not have farmers available to oversee them, however. While farmers can oversee allotment patches, they cannot prevent the nearby herb or flower patches from becoming diseased.

Poison ivy bushes are immune to disease. Farmers will not accept payment to watch over a poison ivy bush.

References

1. Jagex. Mod Ash's Twitter account. 12 April 2019. (Archived from the original on 28 May 2020.) Mod Ash: "Attas affects everything except itself and compost bins. Iasor reduces the chance to 20% of what it would otherwise have been, from what I can see in the code. For Kronos info, I'd suggest trying Kieren."
2. Jagex. Mod Kieren's Twitter account. 7 September 2017. (Archived from the original on 28 May 2020.) Mod Kieren: "So with the release of Ultracompost I figured I'd explain how compost affects crops dying. Sorry it is very word heavy! Fire any questions:)." Note: The image in the tweet says the ultracompost multiplier is 1/7, but later in the thread it is corrected to 1/10. Additionally, the image says "Fruit Trees have 4 chances of becoming diseased" but it's actually five, as can be seen in Apple tree seed for example. Therefore his statement that "fruit trees have a 96.9% chance of surviving" if using ultracompost is incorrect -- it is actually 96.15%. Additionally, collected data shows that it is overwhelmingly likely that when creating the graphic, Kieren adjusted the denominator by one to account for a random roll of 0-127, but did not also adjust the numerator, hence the difference in table by +1.
3. Jagex. Mod Ash's Twitter account. 16 December 2019. (Archived from the original on 16 December 2019.) Mod Ash: "[Does watering crops eliminate chance of disease for one grow cycle stage or just reduce it?] It just reduces it. - [Got it. In that case, how much does watering reduce chance of disease?] There isn't a formula as far as I know - the dev who made the skill just set different numbers."