Has there been any "invasive plants warfare" in the past?

If you're willing to forego the 'warfare' aspect, which given the nature might be difficult to prove, Wikipedia has a list of invasive species, which includes plants.

Assuming the question was inspired by the recent reports of mysterious Chinese seeds arriving in the US and the UK, there's a list of pre-existing invasive species for the UK and for the US. This includes such externally introduced species like Japanese knotweed, Kudzu and Himalayan honeysuckle, which are species found in China.

A number of key features invasive species tend to include are:

• Outcompeting native species
• Growing at a much faster rate due to lack of predator species
• Being difficult or time-consuming to remove
• Containing a noxious or toxic substance, which may also be harmful to humans
• Destroying beneficial species, either by outgrowing or outcompeting them
• Ruining an ecological environment to the point it can no longer recover
• Property damage (E.G. undermining foundational structures)

As other posters have noted, it would take quite a few years to come into effect, however this ignores the possibility that some weaponised plant species may be genetically modified to demonstrate other possible traits.

Plants that have been genetically modified are capable of producing their own pesticides, it wouldn't take much to imagine a modified species that produces something potentially more toxic, that, instead of being geared to insects, is geared towards attacking humans, perhaps, for example, producing neurotoxins in normally edible species, contaminating the food supply.

Historically there doesn't appear to be any ecological warfare to note, but given there have been attempts to weaponise animals (bat bombs, pigeon bombs, remote control dogs), bacteria and viruses, it would be hard not to imagine an attempt to weaponise plants.

Invasive species (not just plants) theory, and the biological knowledge to use it offensively, is relatively new. And, even if attempted, the granting of beneficial outcomes (to the attacker) would lag the initial issue by years, while providing a casus belli from the start if caught. If the situation did not necessarily develop to the attacker's advantage, i.e. if they lost, they'd be stuck paying reparations for decades as they'd have no easy way to "turn off" their attack vector.

Not to mention that, in a number of instances, invasive species were originally intentionally introduced to improve the local situation. So, if miscalculations are common, the reverse (an unintentional benefit to the attacked party) - or at the very least a relative lack of negative effects - could be somewhat expected.

to steal a point from B. Lorentz excellent answer: in the past most enemies were right next to each other, sharing the same ecosystem or with adjacent ecosystems, so the scope for novel invasive species would have been limited.

Last, but not least, historically a good proportion of wars were prosecuted to annex territory. So seeding ecological disruption in what's hopefully soon to be your territory is an additional disincentive.

So a) never heard of that, b) historically not something countries would have thought to try (unlike say flinging plague-ridden corpses into besieged cities) and c) there are many good reasons a country would think twice before using it, unless they were ready to commit to a deeply adversarial relationship for the long haul with limited immediate short term benefits.

re. the article:

But, what’s actually inside seem to be random plant seeds.

Darn sloppy weapon production quality assurance ;-)

Edit: None of this answer is written from the viewpoint that there is ecological warfare going on in the originally linked news story or that the OP believed there was. It's just looking at the practical limitations accounting for the likely lack of historical use.

Another parable put he forth unto them, saying, The kingdom of heaven is likened unto a man which sowed good seed in his field:

But while men slept, his enemy came and sowed tares among the wheat, and went his way.

But when the blade was sprung up, and brought forth fruit, then appeared the tares also.

So the servants of the householder came and said unto him, Sir, didst not thou sow good seed in thy field? from whence then hath it tares?

He said unto them, An enemy hath done this. The servants said unto him, Wilt thou then that we go and gather them up?

But he said, Nay; lest while ye gather up the tares, ye root up also the wheat with them.

Let both grow together until the harvest: and in the time of harvest I will say to the reapers, Gather ye together first the tares, and bind them in bundles to burn them: but gather the wheat into my barn.

Matthew 13:24-30, King James Bible

Obviously this is just a biblical parable, not history, and whatever plant is meant under tares, it was probably native in Iudea, not "invasive". Also it is not speaking about warfare between states, but enmity between individual households.

Nevertheless, this shows that the idea of ruining the enemies crops using plants as biological weapons existed in the ancient world.