# Talk:Disease (Farming)

## Magic trees with ultracompost[edit source]

Mod Kieren's post states the base disease chance for magic trees is 8/128, but using ultracompost reduces that to a tenth (i.e. by 90%), "all divisions are rounded down." It is unclear what he means by "rounded down." Assuming he means the *numerator* in the fraction is divided then rounded down to the nearest integer (which would make sense for fixed point arithmetic)*, the disease probability for magic trees would be (8/128)*(1/10) = 0.8/128 -> 0/128 = 0%. In other words, it would be impossible for magic trees to be diseased when using ultracompost. This is probably unintended. In the same twitter post, Kieren says the ultracompost modifier used to be 1/7, but was changed on 2017-9-8. Using that probability, magic trees with ultracompost would be nonzero. Therefore this problem didn't exist before, but after ultracompost was buffed they didn't realize it would have this effect. This further suggests it is probably a bug.

It is possible Kieren's image is incorrect, and it actually is possible for ultracompost magic trees to be diseased. In that case, someone should be able to prove it with a screenshot taken after Sep 2017. Jagex could also give more info.

\*NB: Before someone disagrees with the "assuming he means the *numerator* in the fraction is divided then rounded down to the nearest integer" said above, this seems to make sense based on two examples Kieren posted on Twitter. First, he said herbs have a base chance of 26/128 being diseased, but it is 1/64 chance with ultracompost. This matches the assumption previously stated: (26/128)*(1/10) = 2.6/128 -> 2/128 = 1/64. Secondly he said fruit trees with ultracompost have a probability of 96.9% of fully growing without protection. This also matches the assumption previously stated: since fruit trees have a base chance of 17/128, the calculation is (17/128)*(1/10) = 1.7/128 -> 1/128, and using the formula in the article, the probability of reaching full growth using that probability is 96.9%, exactly what Kieren gave. Ishiz (talk) 02:21, 26 March 2019 (UTC)

- Thanks to Mitchell's discussion with ModAsh on Twitter. We know that the 8/128 for magic tree is incorrect. https://twitter.com/JagexAsh/status/1143092922511974402 Shoyrukon (talk) 21:44, 24 June 2019 (UTC)

I've suspected the disease rates Kieran gave us weren't quite correct for a while now, so I ran a few experiments to see if it holds up. Of 5,002 herb seeds planted in unprotected patches, treated with ultracompost and without Iasor planted, 345 (~6.9%) of them became diseased. I also planted 1,445 herb seeds with ultracompost and Iasor, and 33 (~2.28%) of those became diseased. With the rates from Kieran, we would expect only 231 (~4.6%) of the non-Iasor influenced patches to become diseased, and 0 of the Iasor influenced patches to become diseased. I'm basing the Iasor numbers on a tweet from Mod Ash confirming that Iasor reduces disease rate to 20% of what it would otherwise be (2 / 5 = 0, rounded down). https://twitter.com/JagexAsh/status/1116719428006236162

My best guess to explain this is that the numbers Kieren gave were actually the base max disease roll. I believe a number between 0 and 127 is generated (128 possible values), and any number that's less than or equal to the max disease roll results in the crop becoming diseased that growth cycle. For herbs, this is 26. 0-26 would be a valid disease roll with no compost (27/128 chances), 0-13 with compost (14/128), 0-5 with supercompost (6/128), and 0-2 with ultracompost (3/128). By including 0 as a valid roll, this essentially makes the rates off by 1. Based on these numbers, we would expect ultracomposted herbs to become diseased ~6.87% of the time. This also helps explain the 0/128 problem with ultracomposted Magic trees, and the 0/128 problem of ultracomposted herbs under the influence of Iasor. If 0 is a valid disease roll, then it explains why Magic trees and herbs still become diseased even when the disease roll is reduced to 0. Arcusaren (talk) 20:25, 7 January 2020 (UTC)

## Extrapolating Yew tree disease rate[edit source]

Since Maples are given 12/128 and Magics 8/128, would it be fair to update the page with Yews as 10/128 (extrapolated)? This way we can show there is a 93% chance of survival. Skimp (talk) 03:10, 19 April 2019 (UTC)