hayake to gaityuu ga hueta.

It is read:

葉焼け（はやけ）と害虫（がいちゅう）が増えた（ふえた）。

So the full reading is:

はやけ と がいちゅう が ふえた。

Here, と means and.

It connects the two nouns:

• 葉焼け = leaf scorch / leaf burn
• 害虫 = harmful insects / pests

So 葉焼けと害虫 means leaf scorch and pests.

In this sentence, と is simply listing two things together.

Because the two nouns are being treated as one combined subject:

• 葉焼けと害虫 = leaf scorch and pests
• が marks that whole phrase as the subject

So Japanese does not need:

• 葉焼けが、害虫が増えた

unless you are making a special stylistic or contrastive point.

The normal phrasing is:

• 葉焼けと害虫が増えた

which means Leaf scorch and pests increased.

が marks the subject of the verb 増えた.

In this sentence, the speaker is presenting what increased:

• 葉焼けと害虫が増えた。
• It was leaf scorch and pests that increased.

Using が sounds natural when you are simply stating a fact or reporting a change.

If you used は instead:

• 葉焼けと害虫は増えた。

it would sound more like a topic, and it may suggest contrast, like:

• As for leaf scorch and pests, they increased.

So が is the more straightforward choice here.

Because 増える is an intransitive verb, meaning to increase or to go up on its own.

• 増える = something increases
• 増やす = to increase something

In this sentence, leaf scorch and pests are the things that increased by themselves, so Japanese uses:

• 葉焼けと害虫が増えた。

If someone actively increased something, then 増やす would be used. For example:

• 農家が作物の生産量を増やした。
• The farmer increased crop production.

So here, 増えた is correct because the subject is what increased.

Because 増える does not take a direct object.

With transitive verbs, you often see を:

• 何かを食べる = eat something

But 増える is intransitive, so the thing that increases is marked with が, not を:

• 人口が増える = the population increases
• 問題が増える = problems increase
• 葉焼けと害虫が増えた = leaf scorch and pests increased

So を would not fit with 増える.

Not always.

増えた is the plain past form of 増える, but Japanese past tense often covers both:

• increased
• has increased

depending on context.

So this sentence could mean:

• Leaf scorch and pests increased.
• Leaf scorch and pests have increased.

Japanese does not always separate simple past and present perfect as clearly as English does. Context tells you which English translation sounds best.

Yes, Japanese often uses 増える not only for countable things, but also for:

• cases
• instances
• frequency
• degree of occurrence

So 葉焼けが増える does not have to mean you are counting individual pieces of leaf burn one by one. It can mean:

• there is more leaf scorch than before
• leaf scorch is occurring more often
• the damage from leaf scorch has become more widespread

The same is true in English when we say things like:

• Disease increased
• Damage increased
• Pest problems increased

So this is perfectly natural Japanese.

No. と has several different uses in Japanese. For example, it can mean:

• and
• with
• a quotation marker
• if/when in some patterns

But in this sentence, because it comes between two nouns:

• 葉焼け と 害虫

it clearly means and.

So you should understand it from context rather than assuming it always has one meaning.

Yes. 増えた is plain style.

A polite version would be:

• 葉焼けと害虫が増えました。

Both mean the same thing, but the tone is different:

• 増えた = plain / casual / neutral written style
• 増えました = polite

The plain style is very common in writing, reports, explanations, and casual speech.

Yes, you could also say:

• 害虫と葉焼けが増えた。

This would still mean the same basic thing.

However, the original order may reflect what the speaker wants to mention first, what feels more natural in context, or what was already being discussed.

So the order can change, but the nuance of emphasis or flow may shift slightly.

Yes, very easily.

Japanese often omits background information that English might state explicitly. For example, this could be understood in a context like:

• This year, leaf scorch and pests increased.
• Because of the heat, leaf scorch and pests increased.
• In the greenhouse, leaf scorch and pests increased.

Japanese frequently leaves out things like:

• time
• place
• cause
• topic already known from context

So although the sentence is short, it can carry a lot of meaning depending on what was said before it.